Desiccation-sensitive Seeds Research Articles

Desiccation-sensitive Hopea odorata seeds: Sensitivity to abscisic acid, water potential and inhibitors of gibberellin biosynthesis

Desiccation-sensitive Hopea odorata seeds: Sensitivity to abscisic acid, water potential and inhibitors of gibberellin biosynthesis

Desiccation tolerance in two species with recalcitrant seeds: Clausena lansium (Lour.) and Litchi chinensis (Sonn.)

AbstractSeeds were collected at weekly intervals from mid-maturation to the fully ripened stage. As seed development progressed, desiccation tolerance increased. Desiccation tolerance of C. lansium seeds was greatest at 67 days after anthesis (DAA), when they tolerated air drying for 9 days; 74 DAA was considered as physiological maturity, and their full viability was only maintained for up to 3 days of drying; overripened seeds (88 DAA) had the lowest desiccation tolerance. In L. chinensis, the desiccation sensitivity of seeds at 98 DAA (fully mature) was higher than that at 84 and 91 DAA (less mature); among the excised embryonic axes at different developmental stages, the less mature ones were less sensitive to desiccation than the fully mature ones; excised embryonic axes of the same stage were more tolerant of desiccation than whole seeds.

International Workshop on Desiccation Tolerance and Sensitivity of Seeds and Vegetative Plant Tissues

International Workshop on Desiccation Tolerance and Sensitivity of Seeds and Vegetative Plant Tissues

‘Dehydrin-like’ proteins and desiccation tolerance in seeds

AbstractThe relationship between tolerance of seeds to extreme desiccation and the presence of ‘dehydrinlike’ proteins was investigated in groups of related taxa from the unrelated plant families Aceraceae and Gramineae. Dehydrin-like proteins were identified by Western blot analysis using an antibody raised against a synthetic oligopeptide representing the 23-amino acid consensus sequence common to all group 2 late-embryogenesis-abundant (LEA) proteins.Evidence is presented that seeds of Acer pseudoplatanus and A. saccharinum are desiccation intolerant (recalcitrant) whereas seeds of A. platanoides and A. rubrum are desiccation tolerant (orthodox). Despite these differences, dehydrinlike proteins at 60 and 20 kDa were detected in all four species.Dehydrins at 20 kDa were also detected in seed samples of two aquatic grasses, Porteresia coarctata and Oryza sativa from the tribe Oryzeae, despite seeds of the former rapidly losing viability on drying, whereas O. sativa is one of the best-known examples of desiccation-tolerant seeds. In O. sativa, there was a correlation between contents of dehydrins detected and the proportion of individuals capable of withstanding extreme drying. However, the possibility of a causal link between these parameters is equivocal. Dehydrin-like proteins were also detected in desiccation-sensitive seeds of Zizania palustris, Z. latifolia and Z. texana and desiccation-intolerant seeds of Spartina anglica, all from the Gramineae.The presence of group 2 LEAs is clearly not diagnostic of desiccation tolerance in seeds. However, a more direct correlation with the expression of other groups of LEAs cannot be discounted.

Indeterminate development in desiccation-sensitive seeds of Quercus robur L.

AbstractFruit and seed development in Quercus robur L. were studied on a single tree over five consecutive seasons. Patterns of growth in the cotyledons and embryonic axes differed between years and resulted in seeds of very different sizes. Moisture content at shedding also differed between years, and late-shed seeds had lower moisture contents than early-shed seeds. Moisture content at shedding was negatively correlated with desiccation tolerance. Seed development in Q. robur therefore appeared indeterminate and did not end in a period of rapid desiccation.Sensitivity to desiccation in Q. robur was not due to an inability to accumulate dehydrin proteins, ABA or soluble sugars, substances that have been linked with the acquisition of desiccation tolerance in orthodox seeds. There were great similarities between several aspects of Q. robur seed development and that of orthodox seeds before the latter entered the terminal phase of rapid desiccation. This pattern of seed development contrasted with that reported for the highly desiccation-sensitive seeds of Avicennia marina.

The expression of dehydrin proteins in desiccation-sensitive (recalcitrant) seeds of temperate trees

Proteins that have homology with dehydrins have been identified immunologically in the desiccationsensitive (recalcitrant) seeds of English oak (Quercus robur L.), European chestnut (Castanea sativa L.), horse chestnut (Aesculus hippocastanum L.), sycamore (Acer psuedoplatanus L.) and silver maple (Acer saccharinum L.), and in the desiccation-tolerant seeds of Norway maple (Acer platanoides L.). The mRNA for a late embryogenesis abundant (LEA) protein (dehydrin) was also detected by Northern blotting, using a cDNA clone (D11) from cotton embryos, in the recalcitrant and orthodox seeds. Medium-stringency washing was required to detect this hybridization. InQ. robur the amount of dehydrin protein increased during seed development, andLEA mRNA was induced by limited desiccation and by abscisic acid. Confirmation of the presence of dehydrin mRNA in matureQ. robur andC. sativa seeds was obtained by in-vitro translation of the extracted polyadenylated RNA followed by analysis of the immunoprecipitation products. Thus the presence of dehydrin proteins is not sufficient to confer desiccation tolerance on truly recalcitrant seeds, nor can their presence or absence be used as clear criteria for identification of recalcitrant seeds.

Free radical activity and loss of viability during drying of desiccation-sensitive tree seeds

SynopsisViability loss during desiccation in the recalcitrant seeds of Castanea saliva, Aesculus hippocastanum and Quercus robur was accompanied by increased lipid peroxidation and build up of a stable free radical within their embryonic axes. We argue that the accumulation of the free radical marks the termination of a series of destructive events following the initiation of oxidative attack during moisture stress in recalcitrant seeds.

Studies on the Development of the Desiccation-sensitive (Recalcitrant) Seeds of Avicennia marina (Forssk.) Vierh.: The Acquisition of Germinability and Response to Storage and Dehydration

Germinability and responses to storage and dehydration were studied throughout the development of the desiccation-sensitive seeds of Avicennia marina. Seeds acquired the ability to produce roots at 55 d after fruit set (DAFS) which is shortly after histodifferentiation, but the capacity for full germinability (seedling establishment) was not attained until 70 DAFS, which is midway through the phase of growth and reserve accumulation. Pre-mature seeds showed a germination lag that was equivalent to the period between harvest and full maturity, but, following short-term storage, this was reduced to that of mature seeds. At no stage, however, would seeds with an intact pericarp germinate.Once seeds were fully germinated, storage lifespan under non-desiccating conditions was independent of developmental stage, but was considerably reduce by the presence of the pericarp, probably because of fungal contamination. Prior to the acquisition of full germination capacity, the seeds were unable to tolerate any dehydration but became tolerant to slight water loss once they became fully germinable, after which desiccation sensitivity was not influenced by the stage of development. If rapidly dried, excised axes of germinable seeds survived to lower water contents than did axes removed from seeds following slower drying.

Seed development in relation to desiccation tolerance: A comparison between desiccation-sensitive (recalcitrant) seeds ofAvicennia marinaand desiccation-tolerant types

AbstractDevelopment of the highly desiccation-sensitive (recalcitrant) seeds of primarily one species,Avicennia marina, is reviewed and compared with the ontogeny of desiccation-tolerant (orthodox) seeds.A. marinaseeds undergo no maturation drying and remain metabolically active throughout development, which grades almost imperceptibly into germination. While PGR control of histodifferentiation is essentially similar to that characterizing desiccation-tolerant seeds, the phase of growth and reserve deposition is characterized by exceedingly high cytokinin levels which, it is proposed, promote a sink for assimilate import. While some starch accumulation does occur, the predominant reserves are soluble sugars which are readily available for the immediate onset of seedling establishment upon shedding. ABA levels are negligible in the embryo tissues during seed maturation, but increase in the pericarp, which imposes a constraint upon germination until these outer coverings are sloughed or otherwise removed. The pattern of proteins synthesized remains qualitatively similar throughout seed development inA. marina, and no LEA proteins are produced. This suggests both that seedling establishment is independent of maturation proteins and that the absence of LEAs and desiccation sensitivity might be causally related. The study onA. marinareveals that for this recalcitrant seed-type, germinationper secannot be defined: rather, it is considered as the continuation of development temporarily constrained by the pericarp ABA levels. This leads to a reexamination of the role of rehydration as key eventsensu stricto, in the germination processes in desiccation-tolerant (orthodox) seeds.

The role of plant growth regulators in the development and germination of the desiccation-sensitive (recalcitrant) seeds of Avicennia marina

AbstractThe contents of the cytokinins zeatin (Z), zeatin riboside (ZR), and isopentenyladenine (IPA), the combined contents of gibberellins1 + 3 (GA), and the contents of indoleacetic acid (IAA) and abscisic acid (ABA) were measured during the development of the desiccation-sensitive seeds of Avicennia marina (Forssk.) Vierh. During the stage of histodifferentiation the amounts of these plant growth regulators (PGRs) were measured on whole fruits. During the phase of seed growth and reserve accumulation measurements were made on the embryonic axis, cotyledons and pericarp separately. Patterns in the amounts of PGRs present during histodifferentiation were similar to those reported for desiccation-tolerant seeds and it suggested that this process is under similar ‘hormonal’ control in A. marina as in orthodox seeds. Very high contents of cytokinins, particularly ZR, were present in both axes and cotyledons during reserve accumulation. This is thought to be related to the nature of the reserves accumulated (soluble sugars), rather than to the phenomenon of desiccation sensitivity. With the exception of ABA, embryonic contents of PGRs were relatively high at seed shedding, consistent with the rapid germination of this highly recalcitrant seed. ABA contents in the embryo were low during reserve accumulation, but concentrations in the pericarp increased throughout this development stage. ABA in the perticap could act to prevent precocious germination. The low concentrations of ABA in the embryo could be related to the desiccation-sensitivity of the seeds of A. marina.

Proteins in development and germination of a desiccation sensitive (recalcitrant) seed species

In the recalcitrant seeds of Avicennia marina, protein content and the rates of protein synthesis increase during histodifferentiation. This is similar to the situation in desiccation tolerant seeds. During the stage of reserve accumulation the protein content and rates of synthesis remain constant and there is no de novo synthesis of proteins which might qualify as storage proteins. There is also no change in the nature of proteins present in either axis or cotyledonary tissues during development or germination. Similarly, fluorographs of axis proteins show only very limited changes in the patterns of protein synthesis during development and germination, at least until the onset of root growth. Heat-stable proteins are present from an early developmental stage. However, no late embryogenic abundant (LEA) proteins are synthesised during the late stages of development, indicating that seedling establishment is independent of such maturation proteins. It is suggested that the lack of desiccation tolerance of A. marina seeds might be related to the absence of desiccation-related LEAs. Although the rate of protein synthesis increases during germination, protein metabolism appears to remain qualitatively the same as that occurring during development. The present results suggest that in these desiccation sensitive seeds, protein metabolism characterising development changes imperceptibly into that of germination.

Changes in ribosomal RNA integrity in leek (Allium porrumL.) seeds during osmopriming and drying-back treatments

AbstractLoss of vigour in leek (Allium porrumL.) seed lots is accompanied by the appearance of damage to ribosomal RNA in quiescent embryo tissue. Polyethylene glycol osmopriming treatments of such low-vigour seed permit replacement of this damaged ribosomal rRNA over a 7-day priming period. Low-vigour leek seeds germinated for 6 days without a prior osmopriming treatment still exhibit evidence of damaged ribosomal RNA in embryo tissue. Osmoprimed leek seeds dried back whilst still in the desiccation-tolerant state retain most of the benefits conferred by priming treatments. Osmoprimed leek seeds dried back when having reached the desiccation-sensitive state germinate poorly, if at all, and exhibit much reduced rates of protein synthesis in embryo tissue upon rehydration compared to desiccation-tolerant seeds. Embryo tissue from dried back, desiccation-tolerant seeds exhibits the capacity for much higher levels of protein synthesis than embryo tissue from unprimed seeds at equivalent stages of imbibition. RNA levels continue to increase in embryo tissue upon rehydration of dried back, desiccation-tolerant leek seeds but not in desiccation-sensitive seeds. Loss of protein synthetic capacity in desiccation-sensitive seeds during rehydration is accompanied by increasing levels of ribosomal RNA degradation. Such ribosomal RNA degradation may be indicative of the germinative capacity of leek seeds dried back after osmopriming treatments.

Germination-associated events and the desiccation sensitivity of recalcitrant seeds ? a study on three unrelated species

The storage behaviour of recalcitrant seeds was assessed using three diverse species: a gymnosperm, Araucaria angustifolia (Bert.) O. Kuntze; a herbaceous monocotyledon, Scadoxus membranaceus (Bak.) Friis Nordal; and a woody dicotyledon, Landolphia kirkii Dyer. Seeds were stored under conditions of high relative humidities that maintained seed moisture content and under low relative humidities that caused drying. At regular intervals moisture content was determined, germinability assessed and the ultrastructure of radicle meristem cells examined. Under storage at high relative humidity, seed moisture content was maintained at the original level and subcellular germination events were initiated in the short-term. Such seeds showed enhanced rates of germination when removed from storage and planted. Long-term storage under these conditions resulted in the initiation of subcellular damage which intensified with time and ultimately resulted in the loss of viability. The rate at which germination events proceeded varied among the three species, and could be directly correlated with the period of viability retention under humid storage conditions. Storage under desiccating conditions resulted in subcellular damage and rapid loss of viability. The rate at which the seeds dried varied among the three species. The proportion of water loss tolerated by the different species before loss of viability, correlated with the rate of drying. The storage behaviour of the seeds of these three species is discussed in terms of a previously described model.

Nondestructive approach for analysing the germinability of acorns

Holm-oak is a sclerophyllous Mediterranean species that presents relatively fast growing, non-dormant, desiccation-sensitive seeds. We investigated the importance of this trait for decreasing acorn predation risk and increasing seedling predation tolerance in combination with delaying the maximal predatory activity of rodents within the seeding season. The study was conducted in a Mediterranean savannah-like forest ecosystem. Temporal changes in acorn availability and predation by mice were studied during the acorn fall period. In a second experiment, propagules at different stages of development (acorns, rooted but un-emerged seedlings and emerged seedlings of different heights) were exposed to rodent predation at the end of the seeding season (end of winter). The results indicated that temporal changes in acorn availability (19–0.05 acorns m−2) and predation rate (0–0.11 acorns day−1) were negatively correlated; the lowest predation rate occurred when the food resource was at its highest (peak acorn fall). The developmental stage reached by propagules at the end of the seeding season significantly affected their ability to escape predation: 52–16% of emerged seedlings escaped predation by mice, but only 6% of rooted, un-emerged seedlings and 2% of acorns did so. Rodent predation of seedlings mostly consisted of cotyledon consumption and its effect on seedling survival was also significantly affected by developmental stage: 70% of emerged seedlings survived predation while only 17% of rooted, un-emerged seedling did so. The acorns did not survive at all. The results reinforce the ecological significance of non-dormancy and the associated rapid seed germination and seedling development facing early recruitment in holm-oak. We suggest that, in environments subject to high rodent predatory activity, early sowing of acorns during the seeding season should be considered in order to maximize the success of forest restoration.

Dehydration Effects on Freezing Characteristics and Survival in Liquid Nitrogen of Desiccation-tolerant and Desiccation-sensitive Seeds

Abstract Dehydration effects on freezing characteristics and survival in liquid nitrogen were studied in 11 species of tropical seeds and in silver maple (Acer saccharinum L.) seeds. Differential thermal analysis was used to determine the threshold moisture level below which seed tissue water was in an unfreezable state. Desiccation-sensitive seeds, areca palm [Chrysalidocarpus lutescens (Bory) Wendl.] and silver maple, did not survive dehydration below the threshold moisture level and did not survive exposure to liquid nitrogen. Nine of 10 desiccation-tolerant seeds [strawberry guava, Psidium cattleianum Sabine; passion fruit, Passiflora edulis f. flavicarpa Deg.; Ceara rubber, Manihot glaziovii Mull. Arg.; dwarf schefflera, Schefflera arboricola (Hayata) Merrill; common guava, Psidium guajava L.; papaya, Carica papaya L., apple of sodom, Solarium sodomeum L.; prickly poppy, Argemone glauca Pope; and seamberry, Sabalparviflora Becc.] survived dehydration to as low as 2% to 12% moisture content (below the threshold moisture levels determined) and in the dehydrated state survived exposure to liquid nitrogen. Coffee (Coffea arabica L. var. Bourbon) seeds tolerated dehydration to as low as 8% moisture content but did not survive exposure to liquid nitrogen. These results demonstrate the feasibility of cryopreserving seed germplasm of several tropical species.

Dehydration Effects on Imbibitional Leakage from Desiccation-Sensitive Seeds

Changes in electrolyte leakage and viability in response to dehydration stress were examined in two species of seeds that do not survive desiccation. Leakage from silver maple (Acer saccharinum L.) seeds increased markedly as seed moisture contents decreased from 45 to 35% (fresh weight basis) and germination decreased from 97 to 5%, coincidentally. Time course curves of imbibitional leakage from areca palm (Chrysalido-carpus lutescens [Bory] Wendl.) embryos showed an increase in both initial leakage and steady-state leakage rates in response to dehydration from an original moisture content of 84 to as low as 53%. Absorbance at 530 nanometers of extracts from triphenyl tetrazolium chloride stained embryos of areca palm was used as a measure of viability. Absorbance decreased significantly in response to dehydration as embryo moisture content decreased from 80 to 30%. Collectively, the data suggest that membranes in the desiccation-sensitive seed tissues studied are damaged by dehydration below a critical moisture content, 40% in silver maple seed and 55% in areca palm embryos, and that the membrane damage contributes to loss of viability.

Effect of Dehydration on Leakage and Membrane Structure in Lotus corniculatus L. Seeds

Membrane damage as a result of dehydration was studied in Lotus corniculatus L. cv. Carroll seeds which had been pregerminated for 0, 12, and 24 hours prior to dehydration. During reimbibition, desiccation-tolerant (0- and 12-hour) seeds leaked relatively low quantities of all solutes (total electrolytes, potassium, phosphate, sugar, amino acid, and protein). Desiccation-sensitive (24-hour) seeds leaked higher levels, but evidence of selective permeability remained. Membrane damage was not manifested as a complete removal of the diffusion barrier, although its permeability properties were dramatically altered. Consequently, the plasmalemma was not ruptured or torn by the dehydration treatment, but a more subtle structural alteration occurred.The possibility that seed membranes form a hexagonal rather than a lamellar phase at moisture contents below 20% was investigated by x-ray diffraction. Phospholipids were extracted from desiccation-tolerant (0-hour) and desiccation-sensitive (24-hour) seeds and hydrated to 5, 10, 20, and 40% water. This phospholipid-water system was examined using low-and wide-angle x-ray diffraction and was found to be exclusively lamellar, even at 5% water. Consequently, membrane damage and the leakage of cytoplasmic solutes from seeds cannot be explained by the formation of a hexagonal phase by membrane phospholipids.