Premature Desiccation Research Articles

First report of Stemphylium leaf blight of onion (Allium cepa) caused by Stemphylium vesicarium in Italy.

In July 2019, severe leaf symptoms were observed on onion plants (Allium cepa L. cv. Dorata di Parma) in a commercial field located in the municipality of Medicina (Bologna, Emilia-Romagna region), in northern Italy. Diseased leaves showed yellowish-pale-brown and oval-shaped lesions, which later coalesced in larger necrotic areas, and black leaf tips. As the disease progressed, conidia developed on the necrotizing leaves, until premature desiccation of the whole plants. Disease incidence of approximately 70% was calculated in the affected field, together with yield losses that were estimated to be above 30%. Symptomatic tissue fragments excised from the leaf lesions were surface disinfested with NaOCl 1% for 2 minutes, rinsed with sterile water and transferred onto potato dextrose agar (PDA). Fungi were consistently isolated after 5 days of incubation at 27 ± 1°C in the dark. Single spore isolation was performed on PDA to obtain 7 pure cultures, whose morphological characteristics were consistent with the description of Stemphylium vesicarium (Ellis 1971). DNA from a representative single spore isolate was extracted and the internal transcribed spacer region (ITS) of ribosomal DNA (rDNA) was amplified using the universal primers P-ITS1 and P-ITS4 (White et al. 1990). The PCR product was sequenced and deposited in GenBank (Accession No. OP144057). A BLAST search in CBS-KNAW collection bank (Westerdijk Fungal Biodiversity Institute, Utrecht, The Netherlands) showed 100% identity for the ITS gene with the strain of S. vesicarium under accession number CBS 124749. Moreover, the PCR assay using the primer pair KES 1999 and KES 2000 (Graf et al. 2016) for the cytochrome b gene displayed the specific fragments of 420 bp for S. vesicarium. The isolate was tested for pathogenicity on onion (potted plants cv. Texas Early Gran, fourth leaf stage) by spraying 4 ml of a conidial suspension (1 × 104 conidia/ ml) per plant. Inoculated and non-inoculated (sprayed with sterile distilled water) plants were kept at 24 ± 1°C and 90% relative humidity with a 16-h photoperiod. Seven days after inoculation, disease assessment was performed. Inoculated plants showed typical Stemphylium leaf blight (SLB) symptoms, similar to those observed in the field. No symptoms developed on the water-inoculated plants. S. vesicarium was consistently reisolated from the artificially inoculated onion plants and identified using a PCR assay, according to Graf et al. (2016). The assay was repeated twice with the same results. SLB is currently reported worldwide and it is considered a re-emerging threat and a truly challenging fungal disease, which can result in yield and quality losses of up to 90% in onion crops (Hay et al. 2021). In Italy, S. vesicarium has been reported several years ago on pear (Ponti et al. 1982) and, more recently, on radish sprouts (Belisario et al. 2008), chili pepper (Vitale et al. 2017) and spinach (Gilardi et al. 2022). To our knowledge, this is the first report of S.vesicarium on onion in Italy. Our results stress that development and implementation of innovative Integrated Pest Management (IPM) strategies are urgently needed to ensure an effective control of SLB, since only a few moderately resistant onion varieties are available (Hay et al. 2021) and no fungicides are currently registered to specifically control SLB in Italy. Further studies are underway to elucidate the pathogen geographic distribution and assess the impact of this disease on the onion crop in Italy.

Mrežaste stenice platana i hrasta

Provides an overview of Sycamore lace bug (Corythucha ciliata Say) and Oak lace bug (C. arcuata Say) based on literature data and monitoring during the period 2018-2022. The species have been present in insect fauna of Serbia over the past fifty years and ten years, respectively. Lace bugs are significant pests of sycamore and oak trees. Their damage manifests itself as premature desiccation and drop of leaf mass (premature defoliation), reducing air quality benefits of trees in urban areas and diminishing aesthetic function. Additionally, tissue injury and loss of nutrients can affect longevity of mature trees and reduce woody mass yield. Presents information on origin and geographic range, biology, damage and control of lace bugs.

High clutch failure rate due to unpredictable rainfall for an ephemeral pool-breeding frog

Animals that reproduce in temporary aquatic systems expose their offspring to a heightened risk of desiccation, as they must race to complete development and escape before water levels recede. Adults must therefore synchronise reproduction with the changing availability of water, yet the conditions they experience to trigger such an event may not relate to those offspring face throughout development, potentially leading to clutch failure. The sandpaper frog (Lechriodus fletcheri) breeds in ephemeral pools that dry within days to weeks after rainfall has ceased. We examined whether spawning frequency and offspring survival differed across two consecutive breeding seasons based on (1) rainfall at the moment of oviposition and throughout offspring development, and (2) pool volume, given their combined effect on hydroperiod. Reproduction was triggered by rainfall, with more spawn laid during periods of greater rainfall and in larger pools. While pool size was a predictor of offspring survival, rainfall during oviposition was not. Rather, follow-up rain events were required to prevent pools drying prior to metamorphosis, with rainfall evenness during development the strongest predictor of reproductive success. High clutch failure rates recorded in both seasons suggest that adults do not have the capability to predict rainfall frequency post-oviposition. We thus conclude that unpredictable rainfall leading to premature desiccation of spawning sites is the primary source of pre-metamorphic mortality for this species. Understanding the influence of rainfall predictability on offspring survival could be critical in predicting the effects of altered hydroperiod regimes due to climate change for species that exploit temporary waters.

Effects of environmental factors and conservation measures on a sand-dune population of the natterjack toad (Epidalea calamita) in north-west England: a 31-year study

A 31-year study monitored Britain’s largest natterjack toad population on the Sefton Coast sand-dune system in north-west England. Key objectives were to describe changes in numbers and breeding success, relate these to environmental variables and explore whether conservation efforts have been well targeted. Considerable variation was found in the number of water bodies used for spawning, the number of spawn strings laid and breeding success based on estimated toadlet production. There was a declining trend in annual totals of spawn strings and toadlets. Positive correlations were established between spring and April rainfall and both spawn count and toadlet production. April rainfall for the study area declined between 2000 and 2017. Premature desiccation of water bodies and associated poor breeding success were frequently observed, there being a positive relationship between water-table height and toadlet numbers. A long-term declining trend in the height of the water-table was established. The mean adult population of Sefton natterjacks was estimated at about 1200 individuals, with a peak around 3150. Successful breeding is increasingly reliant on management to excavate appropriately designed and managed “scrapes” that hold water long enough for metamorphosis to occur. Overgrowth of vegetation and loss of dynamism in the dune system threaten both the natural production of new breeding slacks and the natterjack’s open terrestrial habitat. Encouragement of dune dynamics by removing trees and scrub, increasing areas subject to livestock grazing and mechanical rejuvenation may offer the best hope of conserving this species in the future.

Dissection of jasmonate functions in tomato stamen development by transcriptome and metabolome analyses.

BackgroundJasmonates are well known plant signaling components required for stress responses and development. A prominent feature of jasmonate biosynthesis or signaling mutants is the loss of fertility. In contrast to the male sterile phenotype of Arabidopsis mutants, the tomato mutant jai1-1 exhibits female sterility with additional severe effects on stamen and pollen development. Its senescence phenotype suggests a function of jasmonates in regulation of processes known to be mediated by ethylene. To test the hypothesis that ethylene involved in tomato stamen development is regulated by jasmonates, a temporal profiling of hormone content, transcriptome and metabolome of tomato stamens was performed using wild type and jai1-1.ResultsWild type stamens showed a transient increase of jasmonates that is absent in jai1-1. Comparative transcriptome analyses revealed a diminished expression of genes involved in pollen nutrition at early developmental stages of jai1-1 stamens, but an enhanced expression of ethylene-related genes at late developmental stages. This finding coincides with an early increase of the ethylene precursor 1-aminocyclopropane-1-carboxylic acid (ACC) in jai1-1 and a premature pollen release from stamens, a phenotype similarly visible in an ethylene overproducing mutant. Application of jasmonates to flowers of transgenic plants affected in jasmonate biosynthesis diminished expression of ethylene-related genes, whereas the double mutant jai1-1 NeverRipe (ethylene insensitive) showed a complementation of jai1-1 phenotype in terms of dehiscence and pollen release.ConclusionsOur data suggest an essential role of jasmonates in the temporal inhibition of ethylene production to prevent premature desiccation of stamens and to ensure proper timing in flower development.Electronic supplementary materialThe online version of this article (doi:10.1186/s12915-015-0135-3) contains supplementary material, which is available to authorized users.

Species sorting in space and time—the impact of disturbance regime on community assembly in a temporary pool metacommunity

AbstractEcosystems generally are not stable over long periods of time and are subject to disturbances of different frequencies and intensities. As a result, natural communities usually are not in equilibrium, and temporal snapshots can show different stages of community assembly. Nonequilibrium is especially common in temporary aquatic systems where desiccation continuously resets the development of communities and hydroperiod is an important determinant of species richness and community structure. We investigated effects of disturbance regime on community assembly of aquatic invertebrates in a cluster of 36 temporary rock pools in central South Africa. Pools were assigned to 4 categories based on their long-term disturbance regime and were sampled 4 times during 1 inundation. Disturbance modulated the relative importance of deterministic and stochastic processes driving community assembly and reduced both α and β diversity. Premature desiccation truncated community development. Initial communities were d...

Cell cycle and germination of fresh, dried and deteriorated sugarbeet seeds as indicators of optimal harvest time

AbstractSeeds of sugar beet (Beta vulgarisL.) were collected at weekly intervals from 3 weeks before to 1 week after commercial harvest time, dried and stored at room temperature (18–22°C). Laboratory germination tests and flow cytometric analyses were performed immediately after harvest (fresh seeds) and five times at weekly intervals during storage (dry seeds). After 6 months of storage, seeds were exposed to a controlled deterioration treatment (CD). The proportion of G2nuclei in the embryo was constant in the fresh seeds, regardless of their maturity. It decreased, however, after drying and CD, especially in those seeds harvested before maturation drying had commenced. The proportion of endosperm cells in the seed decreased with maturation, and a further decrease was observed after drying and CD. These observations suggest that nuclei with a higher nuclear DNA content were more sensitive to water stress caused by premature desiccation and to deterioration than nuclei with a lower DNA content. Fresh seeds exhibited some germination, but this increased after drying, suggesting that desiccation induced a switch from the developmental to the germination mode. Germination percentages were the highest in dry seeds collected at the commercial harvest time and a week after. This high germinability coincided with the highest proportion of G2cells in the embryo. It is concluded that flow cytometry provides information about the status of sugarbeet seed maturation, seed quality and storage potential, and can be used for estimation of optimal harvest time.

SDS-insoluble glutenin polymer formation in developing grains of hexaploid wheat: the role of the ratio of high to low molecular weight glutenin subunits and drying rate during ripening

The accumulation of polymeric proteins and the changes in molecular size distribution of these proteins were followed during grain filling and/or premature desiccation. The accumulation behavior of polymeric proteins and their constituent polypeptides (high and low molecular weight glutenin subunits, HMW-GS and LMW-GS) was determined by reversed phase-high performance liquid chromatography using a NaI/propanol purification procedure. With this new extraction and separation procedure, we have demonstrated that there was a coordinated initiation of storage protein biosynthesis, even if the accumulation rate varied greatly between the two main classes of proteins (i.e. monomeric and polymeric fractions). Moreover, the glutenin subunit composition was largely modified during glutenin accumulation. Both the HMW-GS/LMW-GS and HMW-GS-x/HMW-GS-y ratios increased significantly during the whole cell enlargement phase (from 16 to 37 d after anthesis). By applying premature grain desiccation during this physiological phase, we demonstrated that the polymerization index (SDS-insoluble polymers/total polymers) of the glutenin polymers was closely related to the HMW-GS/LMW-GS ratio of these proteins. An increase in the relative proportion of HMW-GS in glutenins caused the proportion of SDS-insoluble polymers to rise during grain desiccation. From these studies, it appears that the modification of the desiccation rate (grain desiccation at a constant temperature with variable relative humidity levels) induced a parallel modification of the glutenin insolubilization rate but did not affect the polymerization index of the glutenins at maturity.

Changes in late-embryogenesis-abundant (LEA) messenger RNAs and dehydrins during maturation and premature drying of Ricinus communis L. seeds.

In Ricinus communis L. (castor bean) endosperms, two classes of Late Embryogenesis Abundant (Lea) transcripts were first detected during mid-development (at 30-35 days after pollination, DAP) and peaked at 50 DAP, just prior to the onset of desiccation. Most of the Class I mRNAs declined substantially during desiccation itself; Class II mRNAs remained abundant in the mature dry (60 DAP) seed. Following imbibition, all Lea mRNAs abundant in the mature dry seed declined rapidly (within 5-24 h). Premature drying of developing 35-DAP seeds resulted in the loss of storage-protein mRNAs (Leg B Mat I); following rehydration, mRNAs encoding post-germinative proteins (Germ D91, D30 and D38) increased in the endosperm. The Lea mRNAs present in the developing fresh seed at 35 DAP were preserved, but did not increase in response to premature desiccation; upon rehydration these Lea mRNAs declined within 5 h. During seed development, substantial changes occurred in the synthesis of a subset of LEA proteins referred to as "dehydrins'; in particular, new dehydrin polypeptides were induced between 40 and 60 DAP. Such proteins were not as evident in prematurely dried endosperms. In contrast to the rapid loss of Lea mRNAs during germination, many of the dehydrin proteins abundant in the dried seed persisted following imbibition or rehydration.

Vicilin and Napin Storage-Protein Gene Promoters Are Responsive to Abscisic Acid in Developing Transgenic Tobacco Seed but Lose Sensitivity following Premature Desiccation.

In transgenic tobacco (Nicotiana tabacum L.) seed, expression of chimeric [beta]-glucuronidase (GUS) genes containing the vicilin or napin storage-protein gene promoters is responsive to premature drying and declines upon rehydration (L. Jiang, W.L. Downing, C.L. Baszczynski, A.R. Kermode [1995] Plant Physiol 107: 1439-1449). Desiccation may cause changes in the content of or sensitivity to abscisic acid (ABA), partially or wholly removing the effects of this "modulator" of developmental gene expression. We studied the enhancement of GUS reporter enzyme activities in transgenic tobacco by exogenous ABA before and after drying. A racemic mixture of ABA at 10 [mu]M caused a 2- to 3-fold increase in GUS activity in developing transgenic seed expressing chimeric genes containing the vicilin or napin gene promoters. However, when these seeds were prematurely dried prior to their culture on ABA medium, enhancement of GUS activity was virtually abolished. Use of optically pure ABAs revealed that the enhancement in GUS activity in developing fresh seed was due largely to the natural (+) form of ABA. Chimeric constructs containing a viral 35S promoter did not respond to ABA whether or not premature drying was applied. Thus, vicilin and napin chimeric genes, initially sensitive to ABA, become relatively insensitive to the hormone following drying. A decline in ABA sensitivity may be an important factor in the cessation of storage-protein gene expression.

Role of desiccation in the termination of expression of genes for storage proteins

AbstractThe final stage of development of orthodox seeds is maturation drying, a process often accompanied by a dramatic decline in storage-protein synthesis. When desiccation is imposed prematurely at certain stages prior to the completion of development, a switch in synthetic events is elicited. events unique to development, such as synthesis of storage protein, are terminated, while syntheses associated with germination and growth are initiated. We investigated whether desiccation plays a key role in effecting a decline in expression of genes for storage proteins by acting directly upon the regulatory regions of these developmental genes. The desiccation responsiveness of the 5′ and 3′ regulatory regions of the gene for the pea storage protein vicilin was tested in transgenic tobacco seed. Chimaeric genes were introduced into tobacco, these genes consisted of the coding region of the reporter gene for β-glucuronidase (GUS) and 5′ and 3′ regions from the vicilin gene, or, as controls, the same regions derived from constitutively expressed genes, presumed to be desiccation-insensitive – those from the cauliflower mosaic virus (35S) and nopaline synthase genes. In transgenic seed expressing the gene constructs containing the vicilin 5′ upstream region, GUS activities declined dramatically after imbibition in mature seed and after rehydration of prematurely dried tobacco seed. In contrast, GUS activities increased after seed rehydration when the constitutive viral (35S) promoter replaced the vicilin 5′ upstream region. The 3′ downstream region of the gene construct did not significantly affect the patterns of changes in GUS activities after seed rehydration. In studies of transient gene expression in castor bean cotyledons, premature desiccation led to termination ofGUSgene expression only when the gene construct contained the vicilin 5′ upstream region. This region may respond directly to desiccation; alternatively, changes totrans-acting factors important for expression of genes for storage-proteins may occur as a result of drying.

Water Status and Development of the Maize Endosperm and Embryo during Drought

Drought during rain filling decreases final kernel mass in maize (Zea mays L.). Lack of assimilates or an unfavorable water status within the embryo or endosperm could limit kernel development. To test these possibilities, remobilization of reduced C and N as well as kernel and embryo water status were measured in plants exposed to a water deficit during rain fill. Irrigation was withheld from field‐grown plants after final kernel number was established. This treatment resulted in a soil moisture deficit of 224 mm and decreased endosperm and embryo mass by 16%, compared with controls. The water deficit shortened the effective filling period, but did not alter the rate of dry matter accumulation in either the endosperm or embryo. Carbohydrate reserves in leaf and stalk tissues as well as N stored in the leaves were remobilized to support kernel growth. However, grain filling ceased before these reserves were depleted completely. Grain filling continued in both well.watered and water‐deficient plants until the moisture content of the endosperm and embryo decreased to 280 and 430 g kg−1 fresh wt., respectively. Water‐deficient plants reached these values 10 d earlier because water loss from the endosperm began sooner after anthesis and maximum water content of the embryo was lower, compared with the controls. Kernel and embryo osmotic potentials (ψs) decreased rapidly late in grain filling and were − 2.2.to − 2.6 MPa when growth ceased. The results indicate that kernel water status is affected directly by drought and may be an important determinant of kernel development. They suggest that a water deficit after anthesis shortens the duration of grain filling by causing premature desiccation of the endosperm and by limiting embryo volume.

Desiccation and the Control of Expression of β-Phaseolin in Transgenic Tobacco Seeds

Drying of seeds at certain stages prior to maturation, i.e. premature desiccation, will terminate synthetic events unique to development, for example, storage protein synthesis, and initiate processes associated with germination. In this study we have investigated the role of desiccation in the expression of a storage protein gene, β-phaseolin, to determine if such a developmentally-regulated gene remains sensitive to drying when controlled by a promoter that has no known sensitivity to this treatment. We compared, in transgenic tobacco seeds, the effects of maturation and premature drying on the expression of a full β-phaseolin gene, and β-phaseolin genes driven by a cauliflower mosaic virus 35S promoter with or without an alfalfa mosaic virus (AMV) 5' untranslated leader sequence

Premature Drying, Fluridone-Treatment, and Embryo Isolation During Development of Maize Kernels (Zea maysL.) Induce Germination, but the Protein Synthetic Responses are Different. Potential Regulation of Germination and Protein Synthesis by Abscisic Acid

Freshly harvested, developing kernels of maize (Zea mays L.) do not germinate up to 77 d after pollination, but can be induced to do so by fluridone, premature desiccation, and isolation of the developing embryo. The pattern of protein synthesis in developing maize embryos is distinct from that during germination and subsequent seedling growth. Premature desiccation at 35 DAP elicits a pattern of protein synthesis upon rehydration which is similar to that in germinated embryos from mature dry kernels. Fluridone-induced viviparous germination is accompanied by changes in the synthesis of some proteins to a post-germinative pattern, but some developmental proteins continue to be synthesized. Embryos isolated from developing kernels at 35 DAP germinate when incubated on water; they also produce some developmental proteins during germination. Kernels from developing cobs at 35 DAP which are detached from the mother plant and maintained in an atmosphere of high relative humidity (moist controls) do not germinate, but neither do they continue a clearly defined pattern of either developmental or germinative protein synthesis. Drying is thus critical to effect a clear transition of protein synthesis from a developmental to a germinative mode in maize embryos. Abscisic acid within the developing embryos is reduced by fluridone, but to a lesser extent by premature drying or maturation drying. Changes in sensitivity to abscisic acid by the developing embryo may be as, or more, important in permitting germination, and the attendant synthesis of proteins, than changes in abscisic acid content.

Distinction between the Responses of Developing Maize Kernels to Fluridone and Desiccation in Relation to Germinability, α-Amylase Activity, and Abscisic Acid Content

Developing kernels of the maize (Zea mays) hybrid W64A x W182E germinated precociously following fluridone treatment. Likewise, following premature drying, the kernels germinated upon subsequent rehydration. Tolerance of the aleurone layer to premature desiccation considerably preceded that of the embryo. The increase in alpha-amylase activity following premature drying was substantial and was equal to, or exceeded, the increase which occurred following normal maturation drying. In contrast, there was only a small increase in enzyme activity, regardless of the concentration of the supplied gibberellic acid, following fluridone treatment. Both fluridone and drying cause a decrease in abscisic acid content within the developing kernels. While this decline in growth regulator may permit kernels to germinate, alone this is not sufficient to permit an increase in alpha-amylase activity. Thus drying is necessary to sensitize the aleurone layer to gibberellin, and thereby elicit enzyme synthesis. For this tissue to achieve its full potential to produce alpha-amylase, it must not only be free of the inhibitory effects of abscisic acid, but it must also be competent to respond to gibberellin.

The Role of Maturation Drying in the Transition from Seed Development to Germination

During mid-development (25–40 d after pollination: DAP) of the castor bean seed the amount of abscisic acid (ABA) increases in both the endosperm and the embryo, declining substantially thereafter until there is little present in the mature dry (60 DAP) seed. Premature desiccation of the seed at 35 DAP also leads to a major decline in ABA within the embryo and endosperm. Partial water loss from the seed at 35 DAP which, like natural and premature desiccation, leads to subsequent germination upon return of the seed to full hydration, causes a much smaller decline in ABA levels. In contrast, ABA declines substantially in the non-dried (hydrated) control at 35 DAP, but the seeds do not germinate. Hence, a clear negative correlation between ABA content and germinability is not observed. Both drying, whether natural or imposed prematurely, and partial drying decrease the sensitivity of the isolated embryo to exogenous ABA by about 10-fold. The protein synthetic response of the castor bean embryo exposed to 0.1 mol m−3 ABA following premature desiccation exhibits some similarity to the response of the non-dried developing embryo—in both cases the synthesis of some developmental proteins is enhanced by ABA, and germination is suppressed. Germination of mature seeds is also suppressed by 0.1 mol m−3 ABA, but the same developmental proteins are not synthesized. In the cotyledons of prematurely-desiccated seed, some proteins are hydrolysed upon imbibition in 0.1 mol m−3 ABA, a phenomenon that occurs also in the cotyledons of similarly treated mature embryos, but not in developing non-dried embryos. Hence the embryo exhibits an ‘intermediate’ response upon rehydration in 0.1 mol m−3 ABA following premature desiccation; viz. some of the responses are developmental and some germinative. Following natural or imposed drying, the isolated embryo becomes relatively insensitive to 0.01 mol m−3 ABA: germination is elicited and post-germinative reserve breakdown occurs in the radicle and cotyledons. The reduced sensitivity of the embryo to ABA as a consequence of desiccation may be an important factor in eliciting the switch to germination and growth within the whole seed.

The Role of Maturation Drying in the Transition from Seed Development to Germination. VI. Desiccation-Induced Changes in Messenger RNA Populations within the Endosperm ofRicinus communisL. Seeds

From 30 to 50 d after pollination (DAP) the total RNA content declines in the developing endosperm of castor bean and only a small amount is present in the mature dry (60 DAP) endosperm. During and following germination of the mature seed the RNA content of the endosperm increases up to 72 h after imbibition (HAI). A similar decline in RNA in the endosperm occurs when the seed is prematurely dried at 35 DAP and there is an increase again upon subsequent rehydration, although not to the level achieved in the endosperm of germinated mature seed. Quantitative and qualitative changes in the mRNA complement of the endosperm occur during development. In particular, messages coding for high mol. wt. proteins (putative storage protein precursors) decline substantially during maturation drying (50-60 DAP). A similar decline occurs as a consequence of premature desiccation at 35 DAP. Following rehydration of these dried seeds the pattern of proteins synthesized in vitro by the mRNAs extracted from the endosperm is very similar to that catalysed by messages from the mature seed endosperm during germination and growth. Some mRNAs associated with development, which persist in the endosperm following natural and imposed desiccation, decline during early imbibition. During germination and growth of mature and prematurely dried seeds a similar complement of mRNAs arise in the endosperm, in an identical temporal sequence. The mRNA for ricin D, a protein synthesized predominantly during development at 30-40 DAP, declines to a low level in the mature dry endosperm (60 DAP) and in that of the prematurely dried seed and does not increase substantially during germination or growth. Thus the changes in protein synthesis effected by drying in the endosperm of castor bean are mediated primarily through changes in their mRNAs, as a result of transcriptional control. Drying, whether occurring naturally or imposed prematurely, results in the permanent suppression of transcription of most developmentally-related messages and, upon subsequent rehydration, the induction of those associated with germination and growth. Some residual mRNAs for developmental proteins which are present in the dry seed are selectively degraded during germination. Thus there are some post transcriptional changes to the mRNA population following drying, in addition to the transcriptional modifications.

The Role of Maturation Drying in the Transition from Seed Development to Germination

lCermode, A. R. and Bewley, J. D. 1988. The role of maturation drying in the transition from seed development to germination. V. Responses of the immature castor bean embryo to isolation from the whole seed: a comparison with premature desiccation.—J. exp. Bot. 39: 487-497. Desiccation is an absolute requirement for germination and post-germinative growth of whole seeds of the castor bean, whether desiccation is imposed prematurely during development, at 35 d after pollination (DAP) or occurs naturally during late maturation (50-60 DAP). Desiccation also plays a direct role in the induction of post-germinative enzyme synthesis in the cotyledons of embryos in the intact seed; this event is not simply due to the presence of a growing axis. Isolation of embryos from the developing castor bean seed at 35 DAP results in both germination and growth, despite the absence of a desiccation event. We have compared the metabolic consequences of premature drying of whole seeds (35 DAP) and isolation of the developing 35 DAP embryos. In both cases, hydrolytic events involved in the mobilization of stored protein reserves proceed in a similar manner and mirror those events occurring within germinated mature seeds. There are differences, however, for post germinative enzyme (LeuN Aase and isocitrate lyase) production occurs to a lesser extent in non-dried isolated embryos than in those from prematurely dried (35 DAP) whole seeds, or from mature dry (whole) seeds. Desiccation of the 35 DAP whole seed does not alter the subsequent response of the embryo upon isolation. Thus, while drying does not affect the metabolism of isolated embryos, it has a profound effect on that of embryos within the intact seed. Tissues surrounding the embryo in the developing intact seed (viz. the endosperm) maintain its metabolism in a developmental mode and inhibit germination. This effect of the surrounding tissues can only be overcome by drying or by their removal. Key words—Metabolism, isolation, desiccation, embryo, endosperm, castor bean, development, germination. Correspondence to: Department of Botany, University of Guelph, Guelph, Ontario NIG 2WI, Canada.

Effects of Rust on Yield and Quality of Pearl Millet Forage1

Rust (Puccinia substriata var. indica) occurs on pearl millet [Pennisetum americanum (L.) Leeke] in most years. Visual effects of the rust are severe, ranging from death of young plants from early infection to premature desiccation and/or death of leaves with later infection. There is a lack of quantitative data on the effects of rust on yield and quality of pearl millet. This study was initiated to assess the effect of rust on yield and quality of individual resistant and susceptible plants. Comparisons of 205 resistant with 173 susceptible plants showed significant reductions in dry matter (DM) concentration, DM yield, and in vitro dry matter digestibility (IVDMD) in diseased plants. The combined effects of lower yields and lower IVDMD led to a mean 51% reduction in digestible dry matter yield from the infected plants. The yield of leaves was reduced less by rust than was the yield of stems, but the opposite was true for IVDMD concentrations. Total sugars in the forage of infected plants were 64% less than in forage of resistant plants. Crude protein concentration was slightly higher in diseased plants. The results clearly demonstrated the benefits to be derived from incorporation of rust resistance into existing or new cultivars of pearl millet.

Reprogramming of Protein Synthesis from a Developmental to a Germinative Mode Induced by Desiccation of the Axes of Phaseolus vulgaris

Immature seeds of Phaseolus vulgaris cv Taylor's Horticultural removed from the pod at 32 days of development do not germinate unless first subjected to desiccation. Our results show that premature drying not only redirects metabolism from a developmental to a germination program but it does so permanently, thus effecting an irreversible switch. This is shown by in vitro protein synthesis, and analysis of poly(A)(+) mRNA with a cDNA probe specific for phaseolin message. For example, the pattern of proteins synthesized in vitro by the mRNA fraction from fresh and prematurely dried axes show strong similarities; on the other hand, the mRNA population from rehydrated axes code for a different set of proteins. Also, the message for phaseolin is preserved following the normal maturation process and premature desiccation of seeds. Following rehydration of immature seeds at the desiccation-tolerant stage, this message is no longer detectable in the axes.