The Selective Abortion Of Seeds And Its Influencing Factors In Two Legume Plants

The phenomenon of"more flowers(ovules)and less fruits(seeds)"often exists in angiosperm.The abortive flowers and ovules have potential reproductive functions.It is a phenomenon that plants develop fruits or seeds through selectively aborting parial young fruits or seeds when the reproductive resources are limited or the improvement of offspring fitness is choosed as a selection power,which is more common in angiosperm,especially in legumes.Melilotus officinalis and Caragana acanthophylla are leguminous forages with wide distribution,having a low seed set rate and specific seed-bearing location.The study on seed set patterns and its influencing factors are helpful to understand the mechanism of seed formation and various reproductive strategies,at the same time,it also lays a theoretical basis for improving crop yield and species protection.Therefore,two different abortion types of legume,Melilotus officinalis and Caragana acanthophylla,were selected as objects to investigate the factors affecting selective abortion of seed in terms of pollination ecology,mating system,resource regulation and seed-bearing pattern before and after ovule being fertilized.The results are as follows:1.Caragana acanthophylla and Melilotus officinalis are two different seed selective abortion types.Caragana acanthophylla has 14±0.14 ovules and forms 2-3 seeds in the ovary,the seeds of the apex and base of the fruit were selectively aborted,while the seeds of the middle part of the fruit were matured.Melilotus officinalis has 6-7 ovules,but most pods form only 1 seed,belonging to the type of forming only one seed at the base by aborting most ovules.2.The development of seeds starts from apical ovule of pod in Caraganaacanthophylla,which begins to expand on the 3^thd after pollination.The abortion of ovules begins in base of pod with about 10%of ovules abortion rate on the 11^thd.A large number of ovule abortion,including the apical ovule fertilized,occurred during12^th-14^thd.Finally,a seed abortion type with low seed setting rate at both ends and high seed setting rate in the middle was formed.It is different from Caragana acanthophylla,the development of seed starts from the ovule in base of pod in Melilotus officinalis,in which the ovules at positions 1 or 2 in base of pod began to expand on the 2^thd after pollinating if the pods are viewed from the peduncular end.Finally,80%of ovules in position 1 can form seeds,and a large number of ovules were aborted behind position 3,in which the abortion of unexpanded ovules occurred on the 4^thd.3.There are general pollination system in both Caragana acanthophylla and Melilotus officinalis with bees as main pollinators,in which some species of the genus Amegilla,Anthophora and Halictus are main pollinators in Caragana acanthophylla and Apis mellifera ligusticais are main pollinators in Melilotus officinalis.There are different mating systems types in two species,in which Melilotus officinalis is highly self-compatible,but need media for pollination,and Caragana acanthophylla is highly self-incompatible.The fluorescence observation of pollen germination and pollen tube growth from different pollen sources in Melilotus officinalis and from natural pollen source of Caragana acanthophylla showed that there were no the phenomenon of pollination limitation in the two species.4.Before fertilization,there was no obvious positional effect on the development of ovules in Melilotus officinalis.The developments of female and male gametophytes were overed in 2-3d before flowering,and the ovule structure showed no cytological abnormalities.The distribution of micropipe related to resource transport also had no obvious position effect before and after fertilization,and they were equally distributed in each ovule after flowering.After fertilization,the top ovules developed firstly in Caragana acanthophylla,but abortion of ovules started from the base of pod.The apical ovules have certain advantages in fertilization time,but its eventually aborted due to the disadvantage of resource allocation.Different from Caragana acanthophylla,the development of seeds start from the ovules in base of pod,and eventually formed mature seeds in Melilotus officinalis.The distribution of pollen tubes in ovary has no obvious position effect.5.Resource regulation shows that early bud were removed during ovule formation can't increase the number of ovules in Caragana acanthophylla,but can significantly increase the number of ovules in Melilotus officinalis.The regulation of resources can not obviously effect on development of ovules before fertilization in Caragana acanthophylla and can not also obviously effect development of ovules after fertilization in Melilotus officinalis.6.The two legume plants have different types of seed selective abortion and its influencing factors.The abortions of seeds were controlled by maternal regulation in Melilotus officinalis,which may be a reproductive strategy to increase seed fitness or seed diffusion ability.The abortion of seed is more influenced by the resource allocation of two reciprocal gradients in Caragana acanthophylla,which is the result of the trade-off between pollen tube distribution and resource transportation.