The Photosynthetic Characteristics Of Sarcotesta Of Seed In Torreya Grandis ’Merrillii’ Associated With Dry Mass During Seed Development

Torreya grandis ‘Merrillii’ is an excellent economic variety of Torreya grandis Fort.ex Lind.The seed development of Torreya grandis ‘Merrillii’ lasts about 17 months.During the seed development,the seed is covered by green sarcotesta which contains abundant chloroplasts.In addition to green leaves,plant can potentially use almost vegetative and reproductive structures to perform photosynthetic CO2 assimilation,which is regarded as an important strategy of additional carbon-acquisition.To define the significance of photosynthesis in seed and the possible cause of its limitation,we investigated the contribution of seed photosynthesis in T.grandis ‘Merrillii’ by measuring its time-course of dry mass,gas exchange,chlorophyll fluorescence parameters,chlorophyll content,nitrogen content and Ru BPC activity.At the same time,the seeds were sprayed with DCMU to further verify the photosynthesis.The main results are as follows:(1)Seed development was divided into three phases: phase one involves the rapid increase of seed size(from 0 to 69 days after protrusion of seed(DAPS));phase two involves the slow down of seed volume increase and a further increase in seed dry mass(from 70 to 138 DAPS);phase three entered the afterripening period(139 to 149 DAPS).The surface area of seed significantly increased by 3.14-fold from27 to 69 DAPS,then slowly increased,and obtained its peak at 138 DAPS.The gross photosynthetic rate(Pg)in seed rapidly decreased from 27 to 69 DAPS,while Pg in its associating current-year leaf dramatically increased from 25 to 95 DAPS.The Pg in seed was significantly higher than that in its leaf from 27 to 69 DAPS,however,the Pg in seed was significantly lower than that in its leaf from 106 to149 DAPS.(2)The contribution of seed photosynthesis to seed carbon requirements increased from 6.29% to 33.3%from 27 to 69 DAPS,followed by a decrease to about 20% until 138 DAPS,then attained the maximum value(about 53.8%)at 149 DAPS,which was by analysis of the time-course of carbon balance in seed.(3)Moreover,we also application the sarcotesta of seed with DCMU(a specific inhibitor of photosynthetic electron transport),and found that the contribution of seed photosynthesis to the dry weight of seed,seed without sarcotesta and oil content was about 25.4,40.0%,25.5%,respectively.,Therefore,we conclude that seed photosynthesis in T.grandis ‘Merrillii’ not only play an important role for seed biomass accumulation during the first and second stages,but also significantly affects its oil content at the after-ripening stage.