Seed abortion in Pongamia pinnata (Fabaceae)

In Pongamia pinnata only one of the two ovules develops into a seed in most of the pods. Since pollen was not found to be limiting and reduced fertilization could not completely explain the observed frequency of seed abortion, it implied an effect of postfertilization factors. Aqueous extracts of developing seeds and maternal tissue (placenta) did not influence abortion in vitro, suggesting that abortion may not be mediated by a chemical. Experimental uptake of ¹⁴C sucrose in vitro indicated that both the stigmatic and the peduncular seed have similar inherent capacities of drawing resources, but the peduncular seed is deprived of resources in the presence of the stigmatic seed. This deprivation of the peduncular seed could be offset by supplying an excess of hormones leading to the subsequent formation of two seeds in a pod. The prevalence of single-seeded pods in P. pinnata seems therefore to be a result of competition between the two seeds for maternal resources. The evolutionary significance of single-seeded pods in P. pinnata is discussed with respect to possible dispersal advantage enjoyed by such pods.     

Patterns of fruit and seed production inBauhinia ungulata (Leguminosae)

Patterns of seed and fruit production ofBauhinia ungulata, a small tree legume indigenous in tropical America, were studied in Costa Rica. Only about 8% of flowers produced fruits. The average pod had 19 ovules and about two thirds of these began seed development, with mature pods containing an average of 9.7 mature undamaged seeds. About half of the mature pods were damaged by herbivores and within these, 27% of ovules or seeds had been eaten. Among trees there was no significant variation in pod production, but the number of ovules per pod and seed production per pod varied significantly. Within infructescences most pods were retained at middle positions. Within pods, the probability of an ovule developing into a seed increased toward the distal end. The pattern of seed and fruit production in this species agrees well in general with that reported for other neotropical legumes. The abortion of seeds and fruits can be regarded as a way of controlling maternal investment, and as a response to herbivory.     

Growth characteristics of Glycyrrhiza glabra cell suspension cultures

Sweet potato (Ipomoea batatas (L.) Lam.) breeding has been hampered by self-and cross-incompatibilities that are frequently encountered among the plants in the section Batatas. Ovule culture techniques were developed to assist in overcoming some of these incompatibilities. Ovules that contain embryos at the late globular to heart shaped stage of development were cultured on MS medium containing full strength or one-half strength salts with 3%, 8% or 12% sucrose. Ovules were cultured either intact or after slicing. Ovules of I. triloba and I. trifida were successfully cultured as early as 3 and 4 days after pollination while sweet potato ovules were successfully cultured 5 and 6 days after pollination. The percentage of ovules with developing embryos on the media tested ranged from 27.8% to 50.2%. The highest percentage of embryos developed when the ovules were sliced and cultured on medium containing one-half MS salts and 8% sucrose. Three plants were recovered from cultured ovules of incompatible interspecific crosses.Abbreviations DAP days after pollination - MS medium Murashige and Skoog (1962) medium     

Seed abortion in wind-dispersed pods of Dalbergia sissoo: maternal regulation or sibling rivalry?

Summary Dalbergia sissoo, a wind-dispersed tropical tree, shows a positively skewed distribution of seeds per pod. This is attributed to the enhanced dispersal advantage of few-seeded pods due to their reduced wing loading (ratio of weight to pod surface area) and low settling velocity. The proximate mechanisms causing the positively skewed distribution were investigated. The distribution could not be attributed to the distribution pattern of ovule number per ovary, pollen grain limitation, lack of ovule fertilization, or post-fertilization elimination of many-seeded pods. Rather, it was caused by the post-fertilization abortion of seeds within a pod 2 weeks after fertilization. This intra-pod seed abortion (IPSA) is due to a dominance hierarchy of fertilized ovules from the distal (near stigma) to the basal end, generated by the temporal differences in fertilization. The dominant developing seeds at the distal end cause the abortion of others through the production and diffusion of an aborting agent. When the dominance hierarchy of the siblings is not intense, pods are formed with more than one seed. We argue that the positively skewed distribution of seeds per pod is not due to maternal regulation but is a result of sibling rivalry. We propose that this sibling rivalry is generated by genetic differences in pollen grain fitness and disucss the results in the context of parent-offspring conflict.     

两种互逆资源梯度影响下刺叶锦鸡儿的种子选择性败育格局

种子的选择性败育在被子植物中普遍存在,开展结籽格局及其影响因素的研究有助于深入了解种子的形成机制及多样化的生殖对策。以刺叶锦鸡儿Caragana acanthophylla为材料,通过传粉过程、胚珠发育动态和资源分配状况的研究,以探讨种子的选择性败育格局及相关影响因素。结果显示：(1)刺叶锦鸡儿具高度自交不亲和性,为泛化的传粉系统,蜂类是主要的传粉者。自然状态的结实率为(86.00±4.96)%,不存在传粉限制,但受精具明显的时间效应。(2)刺叶锦鸡儿单花期4—5d,每朵花有(14.00±0.14)粒胚珠。胚珠的发育从荚果顶部开始,其中,开花后第3天荚果顶部胚珠开始膨大;第11天绝大多数胚珠出现了膨大,此时,在荚果基部的胚珠开始败育,随后荚果顶端受精后的胚珠也出现败育,最终仅荚果中部形成2—3粒种子。其结籽格局为成熟荚果中部胚珠,而败育荚果顶部和基部胚珠的选择性败育类型。(3)受微地形影响,居群内开花植株具斑块分布,对较少开花植株通过添加水肥进行资源调控后,结籽率显著提高,说明在种子形成过程中存在资源限制。综上所述,受精顺序和资源限制两个互逆的资源梯度决定了刺叶锦鸡儿的结籽格局。其中,...     

Developing embryos of Sesbania sesban have unique potential to photosynthesize under high osmotic environment

This study has been carried out to investigate the photosynthetic activities in developing embryos of Sesbania sesban under a highly osmotic environment. In S. sesban, the embryo turns green/chlorophyllous at the early heart shape stage. Interestingly, despite being deeply embedded within the supporting tissues (several layers of pod wall, seed coat and endosperm) and developing in a highly osmotic environment, the growing embryo of the developing seed showed the presence of various components of photosynthetic machinery besides being chlorophyllous. The shade-adaptive nature of the photosynthetic machinery of the embryo is evident from (a) low chlorophyll a/b ratio, (b) photosystem (PS) II attaining maximal activity at low photon flux density and (c) lesser plastoquinone pool. The photosynthetic potential of the growing embryo seems to contribute towards seed filling as it has the potential not only to harvest light energy but also to fix CO2 as efficiently as other photosynthetic parts of S. sesban. In fact, ribulose-1,5 bisphosphate carboxylase purified from embryos manifested subunit composition similar to that of leaves. The PS II activity in leaves, cotyledonary leaves and pod wall declined sharply with increase in the level of NaCl and sucrose above 150 and 300 mmol, respectively. Amazingly, PS II activity in developing embryos was maximal in the presence of 250 mmol NaCl or 500 mmol sucrose and remained high even when NaCl and sucrose levels were increased to 500 and 1000 mmol, respectively. We hypothesize that the developing embryos have some factor(s) which protect(s) the photosynthetic machinery in an environment of high osmotic strength.     

Phloem loading in Vicia faba leaves: Effect of N-ethylmaleimide and parachloromercuribenzenesulfonic acid on H+ extrusion,K+ and sucrose uptake

The effects of a penetrating (NEM) and a non-penetrating (PCMBS) sulfhydryl-specific reagent on proton extrusion, ⁸⁶Rb and [U-¹⁴C]sucrose uptake by Vicia faba leaves have been studied. Proton extrusion was strongly or completely inhibited by 0.1 mM NEM. ⁸⁶Rb and [U-¹⁴C]sucrose uptake were markedly reduced by NEM concentrations equal to or higher than 0.5 mM. Under our experimental conditions, PCMBS (1 mM) exerted a strong inhibition on [¹⁴C]sucrose uptake but did not inhibit proton extrusion and ⁸⁶Rb uptake. The sensitivity of phloem loading to PCMBS is thought to be a consequence of sugar-carrier blockage and not of inhibition of the proton pump.Abbreviations CCCP carbonylcyanide-m-chlorophenylhydrazone - DES diethylstilbestrol - DCCD dicyclohexylcarbodiimide - FC Fusicoccin - NEM N-ethylmaleimide - PCMBS p-chloromercuribenzenesulfonic acid     

种子植物的选择性败育及其进化生态意义

种子植物的选择性败育是指植株在花粉源、传粉次序、果实在植株上的位置和发育果实中的种子数目等因素或者这些因素综合作用的基础上对发育中的幼果或种子选择性败育的现象。植株可以选择性地败育位于果序顶部或基部的果实以及位于果实基部、中部或柱头端的种子。此现象在被子植物中比较普遍,特别是在豆科、十字花科和紫草科中最为常见。导致植物选择性败育的主要原因主要有资源限制和遗传因子两个方面。植物通过选择性败育部分自交或基因型较差的果实或种子,不仅可以提高母本和后代的适合度,而且还可以提高果实或种子的扩散效率。因此,对选择性败育的研究在深入了解植物的结实结籽格局、探讨其进化式样与机制等方面具有重要意义。该文系统总结了国际上有关植物选择性败育的研究工作,重点介绍了选择性败育发生的式样、导致选择性败育的因素、选择性败育的进化生态意义,以及目前研究选择性败育现象的主要方法,并对该领域今后研究前景进行了展望。     

Stigmatic inhibition of pollen grain germination-its implication for frequency distribution of seed number in pods of Leucaena leucocephala (Lam) de Wit

Summary Seed number per pod is negatively skewed in Leucaena leucocephala. Post-fertilisation abortion of pods does not completely explain the skewed distribution. It is shown that a pre-fertilisation regulation effectively restricts the formation of pods with less than a certain number of seeds. The regulation is rendered through the inhibition of pollen grain germination by the stigmatic fluid when the pollen grain is less than a certain critical load in the stigma. Such a control is shown to have implications in the evolution of pollen package units, generation of male gametophytic competition and the economy of packing seeds in pods.     

Selective embryo abortion in a perennial tree-legume: a case for maternal advantage of reduced seed number per fruit

In this study, I analyzed time-course of embryo abortion, positional bias in seed maturation and maternal costs of seed packaging in Cercis canadensis. While basal embryos experience similar rates of abortion as those in other positions during the first week of development, abortion rates peak during the second week. Head start in resource sequestration by stigmatic embryos may explain high rates of basal embryo abortion. Similar seed packaging costs and seed mass for single and multi-seeded pods suggests that maternal parent regulates pod size in accordance with seed numbers per pod investing equally in the surviving offspring. Competition during early developmental period results in the abortion of less competitive embryos allowing for optimal resource investment.     

Self pollination and resource availability affect ovule abortion inCassia fasciculata (Caesalpiniaceae)

We examined the effects of pollen source and resource availability on ovule abortion in the annual legumeCassia fasciculata. Pollen source was controlled by hand-pollinating flowers with cross- or self-pollen. Resource availability to developing fruits was controlled by adjusting fruit loads (heavy versus light) on each plant and exposing plants to different photoperiod cycles (16 vs 12 h of light; short days favor fruit growth at the expense of vegetative growth). In mature fruits the proportion of ovules expanding (showing some development over virgin ovules) ranged from 89–95% and did not increase with resource availability, suggesting that unexpanded ovules were either unfertilized or obligately aborted shortly after fertilization. The proportion of expanded ovules maturing in mature fruits was near 97% for both self- and crosspollinations in the treatment with highest resource availability (light load, short days) and lower in the remaining treatments, where self-pollination resulted in up to 9% lower seed maturation than cross-pollination. In the latter three treatments a pollen source effect was dependent upon the maternal plant; in some plants selfing increased abortion and in others it did not. Collectively, the results suggest that (1) both pollen source and resource availability affect ovule abortion, (2) at least some abortion is facultative, and (3) when resources are limited, self-pollination increases abortion in some but not all maternal plants.     

Structural aspects of ovule and seed development and nonrandom abortion inMelilotus officinalis (Fabaceae)

Summary Only one ovule matures into a seed inMelilotus officinalis. Although eight ovules form within an ovary, only the basal ovule develops into a mature seed, whereas the other ovules degenerate. The investigation of ovule and seed structure at different developmental stages and a comparison of quantitative characters of differently fated ovules within an ovary were undertaken by light, phase contrast, and fluorescence microscopy. In this species, campylotropous ovules develop simultaneously on marginal placentae in an apocarpous unilocular gynoecium. Megasporo- and megagametogenesis proceed normally and are completed in bud. The maturation of the Polygonum type embryo sac takes place after the flower opens. Shortly before fertilization, synergids show signs of degeneration in all ovules. At this stage, neither the structure nor the sizes of ovules within one ovary differ significantly. In spite of this, only the basal ovule develops into a seed. Rarely, one of the upper-situated ovules or the basal and another ovule mature into seeds. Seed enlargement is insignificant until the stage when globular embryo and nuclear endosperm are formed. At the seed-filling stage, other ovules have collapsed and the seed gradually comes to occupy the total volume of the pod. The fruit-to-seed length ratio decreases considerably during seed ripening. At fertilization, ovary length is four times greater than ovule length. In the mature state, the fruit and seed lengths are approximately equal. Seed size and weight diminish with an increase in seed number within a pod, although pod size remains constant. It is assumed that nonrandom abortion of young seeds inM. officinalis is under maternal control and is not related to structural abnormalities in ovule development or with limitation in pollen. We suppose that evolution of this species may have proceeded in the direction of a decrease in seed number and an increase in its sizes, which may play an important role in seed dispersal and seedling establishment.     

Production of seedlings from ovules excised at the zygote stage in Lilium spp.

The present study was undertaken to establish a culture system for ovules excised at the zygote stage in Lilium spp. Ovules of Lilium × `Connecticut King' and L. × `Enchantment' were excised together with placental tissue 3, 5, and 10 days after pollination (DAP) and cultured on B5 medium and half-strength B5 medium containing sucrose at different concentrations. In vitro embryo development in ovules cultured at 3 DAP was influenced by the basal media and the sucrose concentration. The half-strength B5 medium with 9% sucrose was the best condition, but only a few ovules isolated from placental tissue developed into seedlings. Application of embryo culture, in which embryos were excised from ovules after 14 weeks of ovule-with-plancetal-tissue culture, greatly improved the production of seedlings. The present study indicates that a two-step culture procedure, ovule-with-placental-tissue culture and embryo culture, make it possible to produce seedlings from ovules just after fertilization.     

Carbohydrate and nitrogen sources affect respectively in vitro germination of immature ovules and early seedling growth of Impatiens platypetala Lindl.

In vitro germination of 20-day old immature ovules of Impatiens platypetala Lindl. was inhibited at concentrations as low as 50 mM sucrose or mannitol and 100 mM glucose. Younger ovules (12, 14, and 16 days old) were similarly inhibited at 100 mM sucrose.Inorganic nitrogen concentration did not affect germination regardless of ovule age, but seedling fresh weight was significantly less and abnormal development of seedlings was significantly increased by total inorganic nitrogen concentrations higher or lower than 30 mM (at a ratio of 20: 10 mM NO₃ ^-: NH₄ ⁺) in the culture medium.     

EFFECT OF OVULE POSITION IN THE POD ON PATTERNS OF SEED FORMATION IN TWO SPECIES OF LATHYRUS (LEGUMINOSAE: PAPILIONOIDEAE)

Using a combination of observations of fate of ovules in matured fruits and of fluorescence techniques to study pollen tube growth and fertilization of ovules, we examined patterns of seed formation within pods in natural populations of two species of Lathyrus, L. sylvestris and L. latifolius. We also examined variation in these patterns within and among populations and between two consecutive years. In both species, only a portion of the ovules were fertilized. Fertilization occurs over a period of several days and ovules at the stigmatic end of the fruit are the first to be fertilized. Fertilized ovules farthest from the stigma are closest to the maternal nutrition. The pattern of embryo abortion is interpreted as a balance between the early start and genetic quality of embryos near the stigma, on the one hand, and the nutritional advantage of proximity to maternal nutrients, on the other. Differences between the two species in patterns of seed maturation are postulated to be related to differences in breeding system. In L. sylvestris, a higher frequency of selling leads to less genetic diversity of pollen deposited on the stigma, lower competition among potential sires, and a more nearly random pattern of ovule fertilization and maturation within the pod.     

Nitrogen incorporation and remobilization in different shoot components of field-grown winter oilseed rape (Brassica napus L.) as affected by rate of nitrogen application and irrigation

The seasonal course of nitrogen uptake, incorporation and remobilization in different shoot components of winter oilseed rape (Brassica napus L.) was studied under field conditions including three rates of ¹⁵N labelled nitrogen application (0, 100 or 200 kg N ha^-1) and two irrigation treatments (rainfed or watered at a deficit of 20 mm). The total amount of irrigation water applied was 260 mm, split over 13 occasions in a 7-week-period ranging from 1 week before onset of flowering until 4 weeks after flowering.Nitrogen application and irrigation increased plant growth and nitrogen accumulation. Irrespective of N and irrigation treatment more than 50% of total shoot N was present in the stem when flowering started. At the end of flowering, pod walls were the main N store containing about 30–40% of shoot N. The quantities of N remobilized from stems and pod walls amounted in all treatments to about 70% of the N present in these organs at mid-flowering. At harvest, stem and pod walls each contained about 10% of total shoot N, the remaining 80% being incorporated into seeds. The main component contributing to the response of seed N accumulation to nitrogen application and irrigation was pods in axillary racemes. Up to 20 kg N ha^-1, corresponding to about 10% of final shoot N content, was lost from the plants by leaf drop.Irrigation increased the recovery at harvest of applied N from 30% to about 50%, while the level of N application did not affect the N recovery. ¹⁵N labelled (fertilizer derived) nitrogen constituted a greater proportion of the N content in old leaves than in young leaves and increased with age in the former, but not in the latter. Relative to soil N, fertilizer derived N also contributed more to the N content of vegetative than to that of reproductive shoot components. Small net changes in shoot N content after flowering reflected a balance between N import and export, leading to continuous dilution of ¹⁵N labelled N with unlabelled N.     

Influence of 2-deoxy-D-glucose upon growth and invertase activity of carrot (Daucus carota L.) cell suspension cultures

Carrot (Daucus carota L.) cell suspension cultures grew well when provided with glucose, fructose, sucrose or raffinose. Galactose and melibiose supported less growth unless supplemented with glucose or fructose. In combination with ten different sugar mixtures, 2-deoxy-D-glucose (dGlc) inhibited culture growth. Inhibitory effects of dGlc were more marked with fructose, melibiose, raffinose or mixtures of these sugars in the culture medium. The presence of glucose or galactose reduced the inhibitory effects of dGlc on culture growth. Experiments with radioactive labelled sugars demonstrated that dGLc uptake was greater in the presence of fructose than glucose, and that growth inhibition of dGlc coincided with its uptake. Reduced protein content was also associated with the inhibitory effects of dGlc. Cultured cells contained lower levels of invertase (EC 3.2.1.26) activity during the active phase of culture growth (up to 25 days after subculture) than when growth had peaked and subsequently declined. Acid and alkaline invertase activities were not greatly reduced by exogenous hexoses. Invertase activity was greatest during periods of low protein content in all cultures and was inhibited by dGlc during the latter phases of the culture period. Free intracellular sugars throughout the culture period consisted mainly of glucose and fructose.     

Turgor-sensitive sucrose and amino acid transport into developing seeds of Pisum sativum. Effect of a high sucrose or mannitol concentration in experiments with empty ovules

Sugar and amino acid transport into empty ovules of Pisum sativum L. cv. Marzia was examined. In fruits containing 4–6 developing seeds, the embryo was removed from four ovules. After this surgical treatment, each empty seed coat was filled with a solution (pH 5.5) containing a low (0, 50 or 200 m M ), medium (350, 400 or 500 m M ) or high (0.7 or 1 M ) concentration of sucrose and/or mannitol. In pulse-labelling experiments with sucrose and α-aminoisobutyric acid (AIB), transport of sucrose and AIB into an empty ovule filled with a solution containing a high sucrose concentration was the same as transport into an ovule filled with a mannitol solution of similar osmolarity, demonstrating that a high sucrose concentration in the seed coat apoplast affects phloem transport of sucrose and AIB into the seed coat only by the osmotic effect. The osmolarity of a given solution filling the seed coat cavity appeared to be important for phloem transport of sucrose and AIB into empty ovules.
In our experiments, 350 m M appeared to be the optimal concentration for sucrose and AIB transport into the cavity within an empty ovule, giving results comparable with transport into intact ovules. A lower osmolarity of the solution induced less transport. Very high sucrose or mannitol concentrations caused a strong inhibition of sucrose and AIB unloading from the seed coat, so that transport into the empty ovules was inhibited. A low (strongly negative) but not too low osmotic potential of the solution in the seed coat apoplast seems necessary to maintain a normal rate of phloem transport into developing seeds. Apparently, the "sink strength" of developing seeds is turgor-sensitive.     

Involvement of polyamines in the inhibiting effect of injury caused by cutting on K+ uptake through the plasma membrane

The inhibition of K⁺ uptake through the plasma membrane resulting from injury caused by cutting, or from application of polyamines (PAs), has been investigated in root segments of maize (Zea mays L.) and pea (Pisum sativum L.). It was found, for both treatments, that K⁺ uptake recovered if the segments were washed for 2 h. The K⁺ uptake inhibited by cutting and that inhibited by spermidine treatment were stimulated to the same extent by fusicoccin. In addition, there was a correlation between the extent of the recovery of K⁺ uptake caused by washing and the distribution, along the root axis, of both PAs and the activities of enzymes responsible for PA degradation. In apical segments of maize, where the PA content and the activity of the degradative enzyme polyamine oxidase (EC 1.5.3.3) were higher than in the more distal segments, the recovery of K⁺ uptake caused by washing was also higher. On the other hand, the opposite trend was observed in root segments of pea, where the PA content and the activity of the degradative enzyme diamine oxidase (EC 1.4.3.6) were higher in distal segments in which K⁺ uptake was greatly stimulated by washing. The effect of the amine-oxidase inhibitor, aminoguanidine, indicates that the degradation products of PAs are involved in the mechanism of inhibition of K⁺ uptake by PAs. The data also seem to indicate that PAs and their degradation products are responsible for the inhibition of K⁺ uptake occurring as a result of injury sustained by cutting roots into segments.Abbreviations DAO diamine oxidase - FC fusicoccin - PA polyamine - PAO polyamine oxidase - PUT putrescine - SPD spermidine