Cotyledon Cell Number Research Articles

Effects of enhanced UV-B radiation on seed growth characteristics and yield components in soybean

In order to understand the effects of enhanced ultraviolet-B (UV-B) radiation on soybean yield components and seed growth characteristics, three determinate soybean cultivars, Hai339 (H339), Heinong35 (HN35) and Kennong18 (KN18) were grown for 2 years in a field experiment exposed to enhanced UV-B radiation. Enhanced UV-B radiation decreased plant height, dry weight of individual stem and yield per plant of three soybean cultivars on average by 15.5%, 16.9% and 43.7%, respectively. Pod number per plant was the most responsible component for yield change under UV-B radiation in the 2-year study. Seed number per pod was less affected by change in light treatment in our experiment, compared with the pod number per plant. UV-B radiation had no significant effect on effective filling period, however, seed size was negatively impacted by UV-B radiation and it decreased 12.3% for three soybean cultivars. Reduction of seed size was mainly due to the decrease of cotyledon cell number. Enhanced UV-B radiation had no significant effect on cotyledon cell volume, cell growth rate or cell weight. Our results suggested that the reduction of seed ABA concentration was directly responsible for lower cotyledon cell number under enhanced UV-B radiation.

A role for an endosperm-localized subtilase in the control of seed size in legumes.

Here, we report a subtilase gene (SBT1.1) specifically expressed in the endosperm of Medicago truncatula and Pisum sativum seeds during development, which is located at a chromosomal position coinciding with a seed weight quantitative trait locus (QTL). Association studies between SBT1.1 polymorphisms and seed weights in ecotype collections provided further evidence for linkage disequilibrium between the SBT1.1 locus and a seed weight locus. To investigate the possible contribution of SBT1.1 to the control of seed weight, a search for TILLING (Targeting Induced Local Lesions in Genomes) mutants was performed. An inspection of seed phenotype revealed a decreased weight and area of the sbt1.1 mutant seeds, thus inferring a role of SBT1.1 in the control of seed size in the forage and grain legume species. Microscopic analyses of the embryo, representing the major part of the seed, revealed a reduced number of cells in the MtP330S mutant, but no significant variation in cell size. SBT1.1 is therefore most likely to be involved in the control of cotyledon cell number, rather than cell expansion, during seed development. This raises the hypothesis of a role of SBT1.1 in the regulation of seed size by providing molecules that can act as signals to control cell division within the embryo.

Determinism of carbon and nitrogen reserve accumulation in legume seeds

In legume plants, the determination of individual seed weight is a complex phenomenon that depends on two main factors. The first one corresponds to the number of cotyledon cells, which determines the potential seed weight as the cotyledon cell number is related to seed growth rate during seed filling. Since cell divisions take place between flowering and the beginning of seed filling, any stress occurring before the beginning of seed filling can affect individual seed growth rate (C and N reserve accumulation in seeds), and thus individual seed weights. The second factor concerns carbon and nitrogen supply to the growing seed to support reserve accumulation. Grain legume species produce protein-rich seeds involving high requirement of nitrogen. Since seed growth rate as determined by cotyledon cell number is hardly affected by photoassimilate availability during the filling period, a reduction of photosynthetic activity caused by nitrogen remobilization in leaves (e.g., remobilization of essential proteins involved in photosynthesis) can lead to shorten the duration of the filling period, and by that can provoke a limitation of individual seed weights. Accordingly, any biotic or abiotic stress during seed filling causing a decrease in photosynthetic activity should lead to a reduction of the duration of seed filling. To cite this article: N. Munier-Jolain et al., C. R. Biologies 331 (2008).

Soybean (Glycine max) seed growth characteristics in response to light enrichment and shading

Seeds are the primary sinks for photosynthates during reproductive growth. Variation in light intercepted during and after seed initiation has been found a major environmental determinant of soybean [Glycine max(L.) Merrill] seed size. We investigated the influence of light enrichment and shading on seed growth rate, effective filling, cotyledon cell number, cell volume and endogenousABA concentrations of cotyledons/testas during seed filling of soybean. Evans, an indeterminate Group 0 soybean, was subjected to light reduction and enrichment treatments from the beginning of pod formation until final harvest for two years inMassachusetts. Higher rates of seed growth, greater seed dry weight, and higher cotyledon cell number were all observed with light enrichment. There was a reduction in seed growth rate and cotyledon cell number, along with a significant lowering of endogenousABA levels in testa and cotyledon with shade. The level ofABAin cotyledon during seed development was significantly correlated with seed growth rates only under shade treatments. Both the growth rates and seed filling duration were influenced by variation in light interception by the soybean canopy. The effects of varying light treatment on seed size, within one genotype, were most likely due to the differences in seed growth rate and cotyledon cell number.

Growth and development of sunflower fruits under shade during pre and early post-anthesis period

The effect of pre and post-anthesis shading (20% of incident radiation) on pericarp development, cotyledon cell number and seed growth dynamic of fruits from three positions in the capitulum (peripheral, mid and central) of two sunflower ( Helianthus annuus L.) genotypes were studied at two locations. Both shading treatments reduced pericarp weight, fruit volume and total yield per plant. Plants shaded during pre-anthesis maintained the number of filled fruits but reduced their individual weight and cotyledon cell number in the three positions on the capitulum. In contrast, post-anthesis shading reduced the number of filled fruits but their individual weight and cotyledon cell number were reduced only in the central fruits. Sigmoidal functions were fitted to seed growth data to estimate the duration of lag phase, the seed growth rate (SGR) and the effective filling period (EFP). Pre-anthesis shading reduced EFP of peripheral fruits, SGR of mid fruits and SGR and EFP of central ones while post-anthesis shading increased the duration of the lag phase of mid and internal fruits. The hierarchy of fruit growth between positions within the capitulum was not modified by shading treatments and it was associated with differences, among fruit positions, in cotyledons cells number (except between mid and central fruits in pre-anthesis shading) and SGR (except peripheral and mid fruits in post-anthesis shading). SGR not only depended on the cotyledons cell number, which was fixed during the cell division phase of seed development, but it was also sensitive to environmental conditions during the linear phase of growth.

Influence of Microgravity on Ultrastructure and Storage Reserves in Seeds of Brassica rapa L.

Successful plant reproduction under spaceflight conditions has been problematic in the past. During a 122 d opportunity on the Mir space station, full life cycles of Brassica rapa L. were completed in microgravity in a series of three experiments in the Svet greenhouse. Ultrastructural and cytochemical analyses of storage reserves in mature dry seeds produced in these experiments were compared with those of seeds produced during a high-fidelity ground control. Additional analyses were performed on developing Brassica embryos, 15 d post pollination, which were produced during a separate experiment on the Shuttle (STS-87). Seeds produced on Mir had less than 20% of the cotyledon cell number found in seeds harvested from the ground control. Cytochemical localization of storage reserves in mature cotyledons showed that starch was retained in the spaceflight material, whereas protein and lipid were the primary storage reserves in ground control seeds. Protein bodies in mature cotyledons produced in space were 44% smaller than those in the ground control seeds. Fifteen days after pollination, cotyledon cells from mature embryos formed in space had large numbers of starch grains, and protein bodies were absent, while in developing ground control seeds at the same stage, protein bodies had already formed and fewer starch grains were evident. These data suggest that both the late stage of seed development and maturation are changed in Brassica by growth in a microgravity environment. While gravity is not absolutely required for any step in the plant life cycle, seed quality inBrassica is compromised by development in microgravity.

Maternal genotype influences pea seed size by controlling both mitotic activity during early embryogenesis and final endoreduplication level/cotyledon cell size in mature seed.

When reciprocal crosses are made between different pea genotypes, there is a strong maternal influence on mature seed size of the reciprocal hybrids, i.e. their dry weights are similar to that of seeds obtained from their maternal parents. Reciprocal crosses between pea varieties having very different mature seed sizes were used to investigate how the maternal genotype controls seed development and mature seed size. The differences in dry seed weight between genotypes and reciprocal hybrids reflected differences in both cotyledon cell number and mean cell volume, and the maternal control on the establishment of these two traits was investigated. Using flow cytometry, data relative to endoreduplication kinetics in cotyledons during the transition between the cell division phase and maturation were obtained. The appearance of nuclei having an 8C DNA content indicates the initiation of the endoreduplication phenomenon and thus the end of the cell division phase. It was shown that the duration of the cell division phase was the same in the reciprocal hybrids, its value being intermediate between those recorded for their maternal parents. This result indicates that the timing of development of the embryo is not under maternal control, but depends on its own genotype. Consequently, maternal genotype must influence the mitotic rate during the cell division phase to achieve differences in cell number found in the cotyledons of mature F1-reciprocal hybrids. The final level of endoreduplication in cotyledons of mature seeds was also investigated. This study showed that there is a close relationship (r2 = 0.919) between the endoreduplication level in mature cotyledons and seed dry weight or mean volume of cotyledon cells, suggesting that both maternal and non-maternal factors could control the number of endoreduplicating cycles in the cotyledons and, hypothetically, the cotyledon cell size.

Seed growth rate in grain legumes II. Seed growth rate depends on cotyledon cell number

ations in individual seed weight can still account for diVerences in yield between environments for one genoIndividual seed weight and seed growth rate are vari- type, as well as between genotypes in one environment. able within the plant and among environmental condi- Individual seed weight is commonly analysed as the tions. Seed growth rate remains constant during the product of seed growth rate by duration of seed filling. filling period even if assimilate availability is modified. Genotypic diVerences in seed weight are mainly correlated This paper describes the relationship between the with diVerences in seed growth rate ( Egli et al., 1981). In cotyledon cell number fixed at the beginning of seed the companion paper, Munier-Jolain et al. (1998) have filling and the seed growth rate. Two genotypes of pea shown for three grain legume species ( lupin (Lupinus were grown in various environmental conditions: field, albus L.), pea, and soybean) that changes in photoassimglasshouse and growth chamber. One genotype of ilate availability do not aVect seed growth rate if treatsoybean was sown in field. Seed growth rate and coty- ments are applied after the completion of embryo cell ledon cell number were measured. Variations in seed division. A reduction in assimilate availability does not growth rate (0.24 to 1.07 mg per degree-day for pea, lead to a decrease in seed growth rate, whereas total plant 0.23 to 0.42 mg per degree-day for soybean) largely growth and duration of seed filling are reduced. In the account for differences in individual seed weight. For same way, an increase in assimilate availability does not each species, cotyledon cell number (from 3.4◊105 to cause any increase in seed growth rate. Seeds have eVec10.2◊105 per seed for pea, from 6.7◊106 to 9◊106 tively often been described as a high priority sink in per seed for soybean) and seed growth rate are assimilate partitioning (Minchin and Thorpe, 1996). strongly correlated regardless of environmental condi- Thus, assimilate flux in growing seeds fluctuates little and tions and intraplant position. Consequently, seed it can be assumed that seed growth rate remains constant growth rate observed during the seed filling period is during the seed filling period. Consequently, the seed determined before this period during the cell division growth rate observed at the beginning of seed filling in the embryo: variations in seed growth rate depend corresponds to a potential seed growth, which should be on the growing conditions during the period between determined before the period of rapid seed growth. flowering and the beginning of seed filling. Seed development and growth can be divided into three phases (Munier-Jolain et al., 1993). The first one begins

Seed growth rate in grain legumes II. Seed growth rate depends on cotyledon cell number

Seed growth rate in grain legumes II. Seed growth rate depends on cotyledon cell number

Seed size and seed growth rate in relation to cotyledon cell volume and number in common bean

Seed yield is negatively associated with cultivar seed size in common bean ( Phaseolus vulgaris L.). Large-seeded cultivars are predominantly from the Andean center of origin while small-seeded cultivars are from the Mesoamerican center. The objective of this study was to determine the relationship of cotyledon cell number and individual cell volume to seed size and seed growth rate (SGR) in common bean, and to examine the basis for a previously reported decline in seed size and SGR for large-seeded Andean lines when grown in warm environments. Crop growth analyses were conducted with 16 lines of common bean in Palmira (965 m elevation, warm) and Popayan (1850 m elevation, cool), Colombia, and mature seed size, cotyledon cell number and volume per cell were determined. SGR (dry matter basis) increased with both increasing cell number per seed and increasing cell volume. Growth rate per cell was linearly related to cell volume at both sites. The association of large cell size with Andean background was the dominant factor responsible for large seed size and rapid SGR of Andean genotypes. The smaller seed size and SGR of Andean lines at the warmer site appeared to be a result of smaller cell number without compensating increases in cell volume or cell growth rate.

Photoperiodically Induced Changes in Seed Growth Rate of Soybean as Related to Endogenous Concentrations of ABA and Sucrose in Seed Tissues

Short-day photoperiods can increase the partitioning of assimilates to filling seeds of soybean (Glycine max L. Merr.), resulting in higher seed growth rates. The plant growth substance ABA has been implicated in the regulation of assimilate transfer within filling soybean seeds. Thus, we hypothesized that an increased concentration of endogenous ABA in seeds may enhance sucrose accumulation and seed growth rate of soybeans exposed to short-day photoperiods. Plants of cv. Hood 75 were grown in a greenhouse under an 8-h short-day photoperiod (SD) until 11 d after anthesis (DAA) of the first flower, when half of the plants were transferred to a night-interruption (NI) treatment (3 h of low-intensity light inserted into the middle of the dark period). Plants remaining in SD throughout seed development had seed growth rates 43 % higher than that of plants shifted to NI (7-6 mg seed1 d1 vs. 5-3 mg seed1 d1). On a tissue-water basis, the concentration of ABA in SD seeds increased rapidly from 7-6 /tmol I1 at 11 DAA to 65-2 /tmol T1 at 18 DAA, but then declined to 6-6 /jmol I1 by 39 DAA. In contrast, the concentration of ABA increased more slowly in NI seeds, reaching only 47-4 /;mol I1 by 18 DAA, peaking at 57-0 fimo I1 on 25 DAA, and declining to 10-2/tmoll1 by 39 DAA. The concentration of sucrose in SD embryos peaked at 73-5 mmol I1 on 25 DAA and remained relatively constant for the remainder of the seed-filling period. In NI, the concentration of sucrose reached only 38-3 mmol I1 by 25 DAA, and peaked at 61-5 /jmol I1 on 32 DAA. Thus in both SD and NI, sucrose accumulated in embryos only after the peak in ABA concentration, suggesting that ABA may have stimulated sucrose movement to the seeds. The earlier accumulation of ABA and sucrose in SD suggests that ABA may have increased assimilate availability during the critical cell-division period, thus regulating cotyledon cell number and subsequent seed growth rate for the remainder of the seed-filling period.

Cotyledon Cell Number and Size in Birdsfoot Trefoil

Birdsfoot trefoil (Lotus corniculatus L.) has small seed compared with many other forage or grain legumes. Small seed is largely responsible for poor seedling vigor that limits usage of this important forage crop. Factors influencing seed size and cotyledon expansion during seedling growth have not been studied in birdsfoot trefoil. Two studies were conducted to determine if: (i) variation in seed size is due to changes in cotyledon cell number and/or cell size, and (ii) cell division and/or cell enlargement is responsible for cotyledon expansion in growing seedlings. In the first study, cotyledons of MU‐81 and ‘Norcen’ birdsfoot trefoil from three seed‐size classes were macerated in chromic acid. Cells were counted in aliquots of suspended cells. Cell size was estimated by measuring cell area and by calculating the number of cells per milligram of cotyledon dry mass and the dry mass of an individual cell. Cell number per seed increased by 44 and 50% and cell area increased by 47 and 34% from the small to large seed class in Norcen and MU‐81, respectively. In the second study, seeds of MU‐81 were germinated and grown in a growth chamber. The number and area of cells in the expanding cotyledons were measured every 4 d for 20 d using methods similar to the first study, except that cotyledons were pretreated with a dilute pectinase solution prior to maceration in chromic acid. Cotyledon expansion was associated with an increase in cell size but not in cell number. Thus, the maximum size an expanding cotyledon could attain was limited by the number of cotyledon cells in a mature seed and their ability to enlarge.

Source‐Sink Alterations Affect the Number of Cells in Soybean Cotyledons

The ability of an individual soybean [Glycine max (L.) Merr.] seed to utilize assimilate is an important part of the yield production process. Cotyledon cell number is a major determinant of genetic differences in seed growth rate. Experiments were conducted in the field and greenhouse with ‘McCall’, ‘Williams’, and ‘York’ cultivars to determine if source‐sink alterations would affect cotyledon cell number. Source‐sink alteration treatments (66% defoliation, 80% depodding, and 63% insolation reduction) were applied when tagged fruits were 20 to 25 mm long. Seeds from the tagged fruits were harvested at maturity and cotyledon cells were counted. Defoliation or shading reduced cotyledon cell number by 21 to 55% for McCall and York in the greenhouse and Williams in the field. Depodding increased cotyledon cell number by 26 to 102%. Cotyledon growth rates in an in vitro culture system increased with increasing sucrose concentrations and reached a maximum at 100 to 200 mM. Cotyledon growth rates in vitro with saturating levels of sucrose and asparagine were closely correlated with cotyledon cell number across treatments and genotypes. The data indicate that cotyledon cell number in soybean is influenced by the physiological environment during the cell division phase of seed development and that both cotyledon cell number and assimilate supply are important in determining seed growth rate.

An Analysis of Seed Development inPisum sativum

A method for quantifying changes in the cell population of Pisum sativum cotyledons during development is described. The method is based on determining the frequency distribution for cell area following the random sampling of a single-cell suspension of cotyledon cells. The population profile of these cells changed progressively and systematically from a single population, similar in size to meristematic cells, found in embryos less than 3.0 mg in fresh weight, to a bimodal population in embryos greater than 100 mg fresh weight. This method was used to compare embryos of similar size from two genotypes near-isogenic except for genes at the r locus. No significant differences were found between the cell population profiles of embryos up to 30 mg fresh weight. However, a significant difference was found between embryos with fresh weights of 100 mg, the wrinkled (rr) line having a higher mean and maximum cell area (2 951 μm2 and 9 240 μm2 respectively) than the round (RR) line (2591 μm2and 6470 μm2respectively). Comparisons were also made between cotyledon cell populations from round (RR) embryos grown in vivo and in vitro. The most obvious differences were the higher mean and maximum cell size of the large cell population of in vitro grown embryos which were twice those found in vivo. Embryos grown to either 30 mg or 100 mg fresh weight in vitro had a much greater proportion of large cells in the population with a corresponding reduction in total cotyledon cell number, compared with similar sized embryos grown in vivo. These data suggest that comparisons between different genotypes, or, between cultured and in vivoembryos, based on morphological similarities between embryos, may be invalid and subject to misinterpretation.

Relationship of Cotyledon Cell Number and Seed Respiration to Soybean Seed Growth1

Seed Growth rate in soybean [Glycine max (L.) Merr.] is known to be important in determining final yield. Factors influencing growth rate, however, are less well understood. The objectives of this study were to investigate the relationship of cotyledonary cell number and seed component (cotyledons, seed coat, and embryonic axis) respiration to seed growth rate and final seed weight for three field‐grown soybean Plant Introduction (PI) lines with genetic differences in seed weight. They were PI 361.058 (light seeded, 92 mg seed−1), PI 317.336( medium seeded, 225 mg seed−1), and PI 416.845 (heavy seeded, 316 mg seed−1). Seed growth rate varied from 2.6 to 10.0 mg seed−1 day−1, and the number of cells in the cotyledons varied from 4.6 ✕ 106 to 10.3 ✕ 106. The three PI lines examined differed in both rates and duration of cell division in the developing seeds. Seed growth rate and final seed weight were related to number of cells in the cotyledons. However, the relationship was not linear. Growth rate per cell for the heavy seeded line was approximately 67% greater than that for the light seeded line. No relationship was observed between seed growth rate or final seed weight and respiration rates. Respiration rates among PI lines for each seed component decreased similarly during seedfill. Within each PI line, respiration rates decreased faster in cotyledon tissue than in either seed coat or embryonic axis tissue. Our results indicate that seeds having a relatively high number of cells per cotyledon have greater rates of dry matter accumulation and final dry weights, and that these growth characteristics are not associated with increased seed respiration.

DNA contents and cell number in relation to seed size in the genus Vicia

The extent of variation in cell mass, and in the size of the cell population of cotyledons has been examined to determine their relative roles in the evolution of variation in seed weight within the genus Vicia. In the 12 species examined there were highly significant correlations between seed weight and cotyledon cell number, and between seed weight and mean cell mass. The extremes differed by a factor of 625 fold in dry seed weight; of this variation, most (140 fold) was attributable to variation in the size of the cell population and only a 4.47-fold change was due to differences in cell mass. The cotyledon cells of all the species, irrespective of their seed weight showed very high levels of replication of their DNA. The implications of these data in terms of the evolution of seed mass in Vicia is considered. There was a constant relationship between cell mass and DNA amount per cell for all species, irrespective of the basic genome size, extent of DNA replication or of the information content of the genome. The basis of this relationship, and its evolutionary implication, is considered.