Reproductive Buds Research Articles

Seasonal progression of bud dormancy in apricot (Prunus armeniaca L.) in a Mediterranean climate: A single-node cutting approach

The progression of the dormancy of apricot (Prunus armeniaca L.) vegetative and reproductive buds in the summer–winter period (June–March) was analysed with the single-node cutting method during two consecutive years in a Mediterranean climate. The progression of the mean time to budbreak (MTB) was studied. Low MTB values were obtained, which show endodormancy intensity under climatic conditions in the South East of Spain only reached a shallow level in apricot. The onset of bud dormancy occurred prior to the advent of chilling accumulation. Although an oscillating pattern on dormancy progression was observed, MTB increased progressively from summer until January and declined rapidly thereafter coinciding with dormancy breaking, although in 2006–2007, maximum endodormancy intensity was observed at beginning of October. Vegetative and reproductive buds showed a similar pattern of seasonal progression of MTB, although after flower differentiation (ca. September) vegetative buds always showed a deeper dormancy than reproductive buds. Autumn and early winter temperatures seem to play a crucial role over dormancy intensity and dormancy progression. A gradient of increasingly deep dormancy from shoot apex to base is suggested by the gradual increment of MTB in a basipetal direction, although it was influenced by the year.

The Cold Awakening of Doritaenopsis ‘Tinny Tender’ Orchid Flowers: The Role of Leaves in Cold-induced Bud Dormancy Release

Massive flowering of tropical Phalaenopsis orchids is coordinated by the cold-induced release of reproductive bud dormancy. Light and temperature are the two key factors integrated by the dormancy mechanism to both stop and reactivate the meristem development of many other angiosperm species, including fruit trees and ornamental plants. It is well established that leaves and roots play a major role in inducing flower development; however, currently, knowledge of molecular events associated with reproductive bud dormancy release in organs other than the bud is limited. Using differential gene expression, we have shown that the leaves of a hybrid of Phalaenopsis species, Doritaenopsis ‘Tinny Tender’, undergo major metabolic modifications. These changes result in the production of sucrose and amino acids, both of which can sustain bud outgrowth, and auxin and ethylene, which may play important roles in awaking the dormant buds. Intake of abscisic acid and synthesis of the hormone jasmonate may also explain the inhibition of vegetative growth that coincides with bud growth. Interestingly, many genes that were upregulated by cold treatment are homologous for genes involved in flower induction and vernalization in Arabidopsis, indicating that processes regulating flowering induction and those regulating reproductive bud dormancy release may use similar pathways and effector molecules.

Evolution of the PEBP Gene Family in Plants: Functional Diversification in Seed Plant Evolution

The phosphatidyl ethanolamine-binding protein (PEBP) gene family is present in all eukaryote kingdoms, with three subfamilies identified in angiosperms (FLOWERING LOCUS T [FT], MOTHER OF FT AND TFL1 [MFT], and TERMINAL FLOWER1 [TFL1] like). In angiosperms, PEBP genes have been shown to function both as promoters and suppressors of flowering and to control plant architecture. In this study, we focus on previously uncharacterized PEBP genes from gymnosperms. Extensive database searches suggest that gymnosperms possess only two types of PEBP genes, MFT-like and a group that occupies an intermediate phylogenetic position between the FT-like and TFL1-like (FT/TFL1-like). Overexpression of Picea abies PEBP genes in Arabidopsis (Arabidopsis thaliana) suggests that the FT/TFL1-like genes (PaFTL1 and PaFTL2) code for proteins with a TFL1-like function. However, PaFTL1 and PaFTL2 also show highly divergent expression patterns. While the expression of PaFTL2 is correlated with annual growth rhythm and mainly confined to needles and vegetative and reproductive buds, the expression of PaFTL1 is largely restricted to microsporophylls of male cones. The P. abies MFT-like genes (PaMFT1 and PaMFT2) show a predominant expression during embryo development, a pattern that is also found for many MFT-like genes from angiosperms. P. abies PEBP gene expression is primarily detected in tissues undergoing physiological changes related to growth arrest and dormancy. A first duplication event resulting in two families of plant PEBP genes (MFT-like and FT/TFL1-like) seems to coincide with the evolution of seed plants, in which independent control of bud and seed dormancy was required, and the second duplication resulting in the FT-like and TFL1-like clades probably coincided with the evolution of angiosperms.

Systematics and Paleoecology of a New Peltaspermalean Seed Fern from the Triassic Polar Vegetation of Gondwana

A new Triassic seed fern is described on the basis of a large collection of well-preserved plant compressions from the Upper Triassic of Mt. Falla, Queen Alexandra Range, central Transantarctic Mountains. The foliage is simple entire-margined to pinnatifid to partly pinnate and is assigned to Dejerseya lobata (Jones et de Jersey) Herbst emend. nov. Associated with these leaves occur two new reproductive structures. The ovulate organ Matatiella dejerseyi sp. nov. is a lax, conelike structure with primarily shield-shaped megasporophylls that are dissected into three to four narrow lobes, each bearing a single recurved, naked ovule. The pollen organ Townrovia polaris sp. nov. consists of a slender axis arising from a covered reproductive bud, bearing pinnately arranged, stalked, elongate receptacles each with ∼20 unilocular, clavate pollen sacs; the pollen is bisaccate nontaeniate with an irregular longitudinal sulcus and coarse saccus endoreticulations, corresponding to the dispersed pollen Falcisporites australis. Similar pollen grains occur in the micropylar canals of seed cuticles of M. dejerseyi. Co-occurrence data indicate that the three taxa are probably different organs from one plant species. This new seed fern is assigned to the Matatiellaceae, which we place into the Peltaspermales because of structural similarities with vegetative and reproductive organs of other peltaspermalean seed ferns. It appears that several Triassic Gondwanan plant fossil taxa of currently uncertain affinities—such as Pachydermophyllum, Linguifolium, Carpolithus mackayi, and Andersonia—may belong to the Matatiellaceae as well. We suggest that the matatiellacean peltasperms were opportunistic, early successional plants that were particularly successful in colonizing stressed wetland environments in polar latitudes during the Triassic.

High temperatures and time to budbreak in low chill apricot ‘Palsteyn’. Towards a better understanding of chill and heat requirements fulfilment

The efficiency of different temperature cycles in inducing budburst of one-year-old shoots of the apricot cultivar ‘Palsteyn’ from dormancy was evaluated. Three replications of shoots were collected during two consecutive years from adult trees, following the accumulation of different amounts of chilling in the field. Thereafter, shoots were exposed to different temperature cycles in growth chambers, for 60 days. The temperature treatments included a continuous temperature of 5 °C; daily temperature cycles of 19/5 h at 5/15 °C, at 5/20 °C, and at 5/25 °C; and the same temperature cycles for the remainder of the 60-day period, after pretreatment at 5 °C for 30 or 45 days. After the temperature treatments, shoots were forced at 25 °C until budburst. The mean time to budburst (MTB) (in days) of lateral vegetative, terminal vegetative and reproductive buds was evaluated. The efficiency of the different treatments was greatly influenced by the date on which shoots were cut. High temperatures had a more positive effect on the reduction of MTB when chilling accumulation had occurred in the field instead of the growth chamber. After partial chilling accumulation in the field, high temperatures (25 °C) combined with low temperatures are more efficient than cycles of moderate temperatures (15 or 20 °C) to induce an earlier budburst. In view of these results, a parallel accumulation of both chilling and heat requirements after partial chilling accumulation is suggested. The application of these results could assist in the development of more accurate models for the prediction of the overcoming of dormancy and blooming.

Interrupted irrigation and synchronism of reproductive bud development in organic and high density coffee trees (Coffee arabica L.)

This work assessed the impact of interrupted irrigation on the synchronism of reproductive bud development in coffee after pruning of the primary lateral branches and the tree top. The water regimes were: no irrigation; irrigation all year round; irrigation interrupted after 30 days and 15 days before harvesting; and during harvesting for IAPAR 59 and Obata cultivars. The treatments without irrigation and with irrigation all year around reduced the number of flowers and buds. Interrupted irrigation treatments improved the synchronism of coffee bud development. IAPAR 59 and Obata cultivars provided different results, depending on the studied variable.

Two new Dasineura species (Diptera: Cecidomyiidae) from coastal tea tree, Leptospermum laevigatum (Myrtaceae) in Australia

AbstractTwo new species of gall midges, Dasineura strobila Dorchin n.sp. and D. tomentosa Dorchin n.sp., are described from galls in vegetative and reproductive buds of coastal tea tree, Leptospermum laevigatum from Australia and South Africa. Galls cause abortion of buds and, when induced in reproductive tissues, prevent fruit set and seed formation. Despite their assumed relatedness, the two species exhibit clear morphological differences in larvae, pupae and adults of both sexes as well as in the morphology of their galls. These are the first Dasineura species to be described from plants of the Myrtaceae outside the Neotropical and Nearctic regions and the first ones recorded from the chiefly Australian subfamily Leptospermoideae. Given the effect of galls on growth and reproduction of the plant, the gall midges are considered as possible biological control agents of coastal tea tree in areas of Australia and South Africa where the plant is an invasive weed.

THE EFFECTS OF NH4-N AND PLANT GROWTH REGULATORS ON PHALAENOPSIS SPIKING AND FLOWERING

In Phalaenopsis production, year around flowering is possible by temperature control. However, the cost of heating and cooling is high and the development of energy saving methods is a major concern. In this experiment, effects of nitrogen fertilizer and plant growth regulators (PGRs) on spiking were investigated. Nutrient solutions containing 26.2 mg/L NH 4 -N and 82.7 mg/L NO 3 -N (control), control + 140 mg/L NH 4 -N, or control + 140 mg/L Urea-N was applied weekly. Application of excess NH 4 -N delayed flowering by approximately two weeks. Urea-N showed no clear effects on delaying spiking. Naphthalene acetic acid sodium salt (NAA˙Na), Benzyladenine (BA), Thidiazuron (TDZ), gibberellin A 3 (GA 3 ) or s-abscisic acid (s-ABA) was applied to investigate the effects on spiking. Among the PGRs tested, weekly (6 to 16 times) or biweekly (6 to 10 times) applications of 1,000 mg/L NAA˙Na delayed spiking of Phalaenopsis. S-ABA also delayed spiking, more by 6 weekly applications. GA 3 and BA showed no clear effects. TDZ stimulated vegetative or reproductive lateral bud growth markedly, depending on the air temperature. Combined application of NH 4 -N and NAA˙Na 23 times showed clear additional inhibitory effect on spiking. Combined application of NH 4 -N and s-ABA affected inflorescence growth differently, depending on the s-ABA concentrations. To elucidate an efficient and practical NAA˙Na application method, application with a Finnpipette, sprayer, alginic acid or Gelrite gel pellets containing NAA˙Na were experimented. Application with a Finnpipette was the most effective, followed by a sprayer. Application by alginic acid gel showed slight effects, but Gelrite gel showed no effects.

Identification of genes associated with bud dormancy release in Prunus persica by suppression subtractive hybridization

To better understand the molecular and physiological mechanisms underlying maintenance and release of seasonal bud dormancy in perennial trees, we identified differentially expressed genes during dormancy progression in reproductive buds from peach (Prunus persica [L.] Batsch) by suppression subtractive hybridization (SSH) and microarray hybridization. Four SSH libraries were constructed, which were respectively enriched in cDNA highly expressed in dormant buds (named DR), in dormancy-released buds (RD) and in the cultivars with different chilling requirement, 'Zincal 5' (ZS) and 'Springlady' (SZ), sampled after dormancy release. About 2500 clones picked from the four libraries were loaded on a glass microarray. Hybridization of microarrays with the final products of SSH procedure was performed in order to validate the selected clones that were effectively enriched in their respective sample. Nearly 400 positive clones were sequenced, which corresponded to 101 different unigenes with diverse functional annotation. We obtained DAM4, 5 and 6 genes coding for MADS-box transcription factors previously related to growth cessation and terminal bud formation in the evergrowing mutant of peach. Several other cDNAs are similar to dormancy factors described in other species, and others have been related to bud dormancy for the first time in this study. Quantitative reverse transcription polymerase chain reaction analysis confirmed differential expression of cDNAs coding for a Zn-finger transcription factor, a GRAS-like regulator, a DNA-binding protein and proteins similar to forisome subunits involved in the reversible occlusion of sieve elements in Fabaceae, among others.

Two Reproductive Bud Thinning Alternatives for Cactus Pear

Cactus pear (Opuntia spp.) is an important Mexican fruit crop cultivated extensively (about 51,000 ha) in the semiarid highlands of Mexico. Fruit exports have increased in the last decade, but to fulfill these markets, fruit size must be enhanced. However, current hand thinning reduces yield, thus making it uneconomical for growers. The objective was to evaluate two reproductive bud (RB) thinning protocols in an effort to increase export fruit size without depressing cactus pear yield. Two experiments were conducted during the 2004 growing season with two cactus pear types: Cristalina (Opuntia albicarpa) and Rojo liso (Opuntia ficus-indica). In the first experiment, the treatments were no thinning (control) or keeping 4, 8, or 12 RBs per cladode. In the second experiment, the treatments were no thinning (control), thinning every other bud along the cladode, and thinning two of every three buds along the cladode. In the first experiment, yield of Cristalina was reduced by 10.4% and 51.8% when eight or four RBs per cladode were retained, respectively. Mean fruit weight of Cristalina decreased with the most severe thinning treatment. Yield of Rojo liso was reduced when four RBs were retained per cladode. In the second experiment, yield of both cactus pear types was unaffected by the thinning treatments. Therefore, we recommend thinning every other bud along the cladode because it does not reduce yield and tends to improve marketable fruit in both cactus pear types. However, this thinning alternative should be tested in other commercial cactus pear types if growers are interested in export markets.

Effect of elevated CO 2 on vegetative and reproductive growth characteristics of the CAM plants Hylocereus undatus and Selenicereus megalanthus

This study examined the vegetative and reproductive growth responses of the crassulacean acid metabolism (CAM) vine-cactus fruit crop species Hylocereus undatus and Selenicereus megalanthus to CO 2 enrichment (1000 μmol mol −1 vs. control of 380 μmol mol −1). H. undatus plants enriched with CO 2 demonstrated 52%, 22%, 18%, and 175% increases, relative to plants measured in ambient CO 2, in total daily net CO 2 uptake, shoot elongation, shoot dry mass, and number of reproductive buds, respectively. The responses of S. megalanthus plants exposed to elevated CO 2 were greater than those of H. undatus under the same conditions. Compared to plant responses in ambient CO 2, under conditions of CO 2 enrichment, S. megalanthus showed 129%, 73%, 68%, and 233% increases in total daily net CO 2 uptake, shoot elongation, shoot dry mass, and number of reproductive buds, respectively. Moreover, for H. undatus, there was no significant change in fruit fresh mass although it showed a slight (7%) upward trend. On the other hand, fruit fresh mass of S. megalanthus significantly increased by 63% in response to elevated CO 2. These results indicate the high potential of CAM plants to respond to CO 2 enrichment. It is thus apparent that S. megalanthus grown under CO 2 enrichment may benefit from elevated CO 2 to a greater extent than H. undatus grown under sub-optimal growth conditions.

Altered sucrose metabolism impacts plant biomass production and flower development

Nicotiana tabacum (tobacco) was transformed with three genes involved in sucrose metabolism, UDP-glucose pyrophosphorylase (UGPase, EC 2.7.7.9), sucrose synthase (SuSy, EC 2.4.1.13) and sucrose phosphate synthase (SPS, EC 2.4.1.14). Plants harbouring the single transgenes were subsequently crossed to produce double and triple transgenic lines, including: 2 x 35S::UGPase x SPS, 4CL::UGPase x SPS, 2 x 35S::SuSy x SPS, 4CL::SuSy x SPS, 2 x 35S::UGPase x SuSy x SPS, and 4CL::UGPase x SuSy x SPS. The ultimate aim of the study was to examine whether it is possible to alter cellulose production through the manipulation of sucrose metabolism genes. While altering sucrose metabolism using UGPase, SuSy and SPS does not have an end effect on cellulose production, their simultaneous overexpression resulted in enhanced primary growth as seen in an increase in height growth, in some cases over 50%. Furthermore, the pyramiding strategy of simultaneously altering the expression of multiple genes in combination resulted in increased time to reproductive bud formation as well as altered flower morphology and foliar stipule formation in 4CL lines. Upregulation of these sucrose metabolism genes appears to directly impact primary growth and therefore biomass production in tobacco.

On buds man

The nature of scaly buds, homologies of their bud scales and degrees of preformation of contained leaf primordia are briefly described. Distinction is made among vegetative, reproductive, mixed, latent, and adventitious buds. Character of buds as associated with position along and around their supporting shoots and with relative vigour of those supporting shoots is discussed. Reference is made to how knowledge of buds and their fates is useful not only in species identification but also in understanding and modelling development of tree crowns, and in how inter- and intra-generic differences must be accounted for when devising measures to affect development in tree crowns. Key words: bud-scale homology, conifers, hardwoods, lateral buds, leaf primordia, long-shoot versus short-shoot buds, position on shoots, pseudoterminal buds, reproductive buds, terminal buds, vegetative buds

PHOTOSYNTHESIS AND SINK ACTIVITY OF WASP-INDUCED GALLS INACACIA PYCNANTHA

Although insect galls are widely known to influence source-sink relationships in plants, the relationship between photosynthesis and gall activity has not been extensively studied. In this study we used 14CO2, photosynthesis, and respiration measurements to examine the capacity of bud galls induced by the wasp Trichilogaster signiventris (Pteromalidae) as carbon sinks in Acacia pycnantha. Galls of this species develop either in vegetative or reproductive buds, depending on the availability of tissues at different times of the year, and effectively eliminate seed production by the plant. Photosynthetic rates in phyllodes subtending clusters of galls were greater than rates in control phyllodes, a result we attributed to photosynthesis compensating for increased carbon demand by the galls. Contrary to previous studies, we found that photosynthesis within galls contributed substantially to the carbon budgets of the galls, particularly in large, mature galls, which exhibited lower specific respiration rates allowing for a net carbon gain in the light. To determine the sink capacity and competitive potential of galls, we measured the proportion of specific radioactivity in galls originating from either vegetative or reproductive buds and found no difference between them. The proportion of the total amount of phyllode-derived 14C accumulated in both clustered and solitary galls was less than that in fruits. Galls and fruits were predominantly reliant on subtending rather than on distant phyllodes for photosynthate. Solitary galls that developed in vegetative buds constituted considerably stronger sinks than galls in clusters on inflorescences where there was competition between galls or fruits for resources from the subtending phyllode. Wasps developing in solitary vegetative galls were correspondingly significantly larger than those from clustered galls. We conclude that, in the absence of inflorescence buds during summer and fall, the ability of the wasps to cause gall formation in vegetative tissues tempers intraspecific competition and substantially increases the availability of plant resources for the development of wasps in such galls.

(102) The Dynamic Model and Rest-breaking Agents in California `French' Prune Production

Use of rest-breaking chemicals may partially substitute for chill requirement in “French' prune. Many California prune growers use oil in the dormant season to tighten and advance bloom, with application timing judged by experience and calendar date. Other rest-breaking agents have become commonly used in California cherry production and their application is generally timed by chill portion accumulation, calculated by the Dynamic Model. We evaluated the effects of treatments of dormant oil or CAN17 (calcium ammonium nitrate) + Entry on budbreak and bloom progression in `French' prune with applications timed at regular intervals. While most treatments improved fruit set and reduced reproductive bud death, an optimum range for both types of rest-breaking treatments was found for advancement and compression of bloom. All rest-breaking treatments advanced fruit maturity equally, compared to the untreated control, as measured by fruit firmness. Although chill hour (hours ≤7°C) calculations might also be used for timing these treatments, when chill portion and chill hour accumulations are compared for the 2004–05 dormant season at several different sites, differences from site-to-site are small for chill portions, and much greater for chill hours. This fact supports experimental evidence from numerous California trials in sweet cherry in which rest-breaking treatment timings based on the Dynamic Model tend to be more consistent than the timings based on the “chill hour” model.

(93) Vegetative and Flower Bud Development, and Fruit Set of Low-chill Peach Cultivars in North-central, Central, and Southwest Florida

Four low-chill peach cultivars were evaluated at three locations in Florida for vegetative and reproductive bud development and fruit set. Twenty trees (five each of `Flordaprince', `Tropicbeauty', `UFgold', and `Flordaglo') were planted at each site in Feb. 2002. Prior to budbreak in Spring 2004 and 2005, three shoots per tree of average length and diameter were selected at a height between 1.5–2.0 m and the numbers of vegetative and flower buds per node were recorded for each shoot. No consistent pattern for the number of vegetative buds per node was observed among cultivars and locations, or across years. However, 'Tropicbeauty' tended to have fewer vegetative buds per node than `Flordaprince' during both seasons, although not at all locations. Overall, the number of flower buds per node was greater for north-central Florida than for central or southwest Florida. There were no consistent tends over years and among locations for the ranked order of flower buds per node by cultivar. The percentage of nodes without flower or vegetative buds (blind nodes) was generally greatest for `Tropicbeauty' at most locations during both years. During 2005, the percentage of blind nodes was greater in central and southwest Florida than in north-central Florida. Overall, fruit set was similar between the central and north-central Florida locations. Fruit set tended to be higher for `UFGold' and `Flordaglo' than for `Flordaprince' or `Tropicbeauty'.

Gibberellic Acid Inhibits Floral Bud Induction and Improves `Bing' Sweet Cherry Fruit Quality

This paper reports on the potential of gibberellic acid (GA3 and GA4+7) to reduce sweet cherry (Prunus avium L.) floral bud induction and balance fruit number and improve fruit quality in the season following application. In 2003, GA3 was applied to `Bing'/`Gisela 1' trees at 50 and 100 mg·L-1 at the end of stage I of fruit development, end of stage II, and on both dates. These treatments were compared to the industry standard application of 30 mg·L–1 applied at the end of stage II and an untreated control. Fruit quality was evaluated in the year of application (i.e., nontarget crop) and return bloom, fruit yield and quality were assessed in the subsequent season (2004). In 2003, GA3 delayed fruit maturity proportional to rate. In 2004, bloom density and fruit yield were related negatively and linearly to GA3 concentration. GA3 reduced the number of reproductive buds per spur and did not affect the number of flowers per reproductive bud. Nonspur flowering at the base of 1-year-old shoots was more inhibited by GA3 than flowering on spurs. Double applications significantly reduced bloom density and yield versus single applications. Trees treated with two applications of 50 and 100 mg·L–1 yielded fruit with 7% and 12% higher soluble solids, 15% and 20% higher firmness, and 7% and 14% greater weight, respectively. However, no treatment improved crop value per tree. In a separate isomer trial, GA3 and GA4+7 were applied to `Bing'/`Gisela 1' trees at 100 and 200 mg·L–1 at both the end of stage I and II in 2004. GA3 and GA4+7 applied at 100 mg·L–1 reduced bloom density similarly by 65%. GA3was more inhibiting than GA4+7at 200 mg·L–1, reducing bloom density by 92% versus 68%. We observed a 4- to 5-day delay in flowering from both GA formulations at 200 mg·L–1. At both concentrations, GA3 reduced yield by 71% and 95% versus 34% and 37% reduction by GA4+7. Fruit weight and soluble solids were unaffected but fruit firmness was increased by all treatments (6% to 17%). However, crop value per tree was highest from untreated control because improvements in fruit quality were insufficient to offset reductions in yield. GA3 shows potential as a novel crop load management tool in productive `Bing' sweet cherry orchard systems.

Timing and Severity of Postharvest Water Stress Affect Following-year Productivity and Fruit Quality of Field-grown `Snow Queen' Nectarine

The effects of the timing and severity of postharvest water stress on the productivity and fruit quality of field-grown nectarine [Prunus persica (L.) Batsch cv. Snow Queen] were studied for two consecutive years. Three levels of postharvest water status (midday stem water potentials of -1.2, -2.0, and -2.8 MPa) were examined. They were designated as High, Med, and Low, respectively. In the second year two additional treatments were examined in which Low and Med water status were interchanged on 1 Sept. 2002, and these treatments were designated as Low/Med and Med/Low. The percentages of double fruits and of those having a deep suture increased with decreasing postharvest midday stem water potential during the previous year, and most of these defects were stimulated by water deficits that occurred prior to 1 Sept. Postharvest water stress led to decreased crop yield in the subsequent year because there were fewer fruits per tree. Flower buds with double pistils were first noticed in mid-September, and by mid-November the ranking of double pistils in the various treatments were similar to the ranking of double fruits measured a month after bloom in the subsequent season. Postharvest water stress delayed flower bud development. The percentage of double fruits increased from 10% in 2002 to 40% in 2003 and the higher percentage in 2003 was associated with higher air temperatures during the reproductive bud development stage in 2002 than in 2001. Our data and others suggest that high temperatures create a potential for the occurrence of double fruits, but that the fulfillment of that potential is highly dependent on postharvest tree water status. The occurrence of double and deep suture fruits were highly correlated with midday stem water potential in August of the previous year, i.e., during the initial stages of flower bud development. The occurrence of double fruits was observed to increase sharply as the midday stem water potentials fell below -2.0 MPa, which suggests that a midday stem water potential of -2.0 MPa could serve as a threshold for postharvest irrigation scheduling.

Constitutive expression of the SAP1 gene from willow (Salix discolor) causes early flowering in Arabidopsis thaliana

SAP1-1 and SAP1-2 were isolated from the male reproductive buds of willow (Salix discolor, clone S365). SAP1-1 differs from SAP1-2 based on a few nucleotide substitutions, but the sizes of their full-length cDNAs are identical. The deduced amino acid sequences of SAP1-1 and SAP1-2 were 98% similar and contain the same C-terminal amino acid motif "GYGA" like that of PTAP1-2 from Populus trichocarpa. The expression patterns of SAP1 in various parts of the male reproductive buds of S. discolor implicate this gene in the formation of the inflorescence meristems, bracts, and floral meristems. To characterize the functions of SAP1, we assessed Arabidopsis thaliana transformed with 35S: :SAP1-1. A total of 52 transgenic T1 lines were obtained, and a 3:1 segregation ratio was obtained in the T2 generation of each line. In the T3 generation, five homozygous transgenic lines were obtained, which were used for further analysis. Screening of transgenic lines was greatly facilitated by the detection of GFP expression starting with germinating seeds. Phenotypes of the homozygous transgenic lines included early flowering, conversion of inflorescence branches to solitary flowers, formation of terminal flowers, and formation of flowers with greater number of petals, stamens, and pistils. Northern analysis showed similar expression levels in all five lines. This study provides the first functional analysis of an APETALA1 (AP1)/SQUAMOSA (SQUA) homolog from a dioecious species and suggests that SAP1 is a homolog of the AP1/SQUA gene.

The tropical cedar tree (Cedrela fissilis Vell., Meliaceae) homolog of the Arabidopsis LEAFY gene is expressed in reproductive tissues and can complement Arabidopsis leafy mutants

A homolog of FLORICAULA/LEAFY, CfLFY (for Cedrela fissilis LFY), was isolated from tropical cedar. The main stages of the reproductive development in C. fissilis were documented by scanning electron microscopy and the expression patterns of CfLFY were studied during the differentiation of the floral meristems. Furthermore, the biological role of the CfLFY gene was assessed using transgenic Arabidopsis plants. CfLFY showed a high degree of similarity to other plant homologs of FLO/LFY. Southern analysis showed that CfLFY is a single-copy gene in the tropical cedar genome. Northern blot analysis and in situ hybridization results showed that CfLFY was expressed in the reproductive buds during the transition from vegetative to reproductive growth, as well as in floral meristems and floral organs but was excluded from the vegetative apex and leaves. Transgenic Arabidopsis lfy26 mutant lines expressing the CfLFY coding region, under the control of the LFY promoter, showed restored wild-type phenotype. Taken together, our results suggest that CfLFY is a FLO/LFY homolog probably involved in the control of tropical cedar reproductive development.