The Caryopsis Growth And The Endosperm Cell Development In Wheat And Maize

To make clear the growth of the caryopsis and the development of endosperm cell in wheat and maize, the caryopses of two wheat cultivars, Zhengmai9023and Yangmai19, and two maize cultivars, Nongle988and Yangnuol, were used as materials in this study. The caryopses developments days were carefully recorded to observe the caryopses growth. The histochemical staining methods were used to detect the activity of endosperm and the content of starch. The morphology and structure changes of endosperm cell and amyloplasts were observed by using resin semi-thin sections and combined with light microscope and scanning electron microscope. The results were listed as below.1The caryopses growth and endosperm cell development in wheat(1) The pericarp of wheat caryopsis was abundant with chloroplasts at early and middle development stage which appeared green. The chloroplasts disappeared at later stage and.the pericarp changed from green to yellowish-white. The changes of length, width, thickness, fresh weight and dry weight of caryopsis present S-curve. The length, width and thickness of caryopsis were basically stabled at16day after flowering. The increasing rate of fresh weight and dry weight slowed down after24day. The moisture content of caryopsis was between70%～80%at early development stage while in lower content at later stage. The size, weight and moisture content of caryopsis in two wheat cultivars were Zhengmai9023>Yangmai19.(2) The morphogenesis process of endosperm included the free nuclei stage and the cellularization stage. The free nuclei stage of Zhengmai9023occured at0-2day after flowering, and the cellularization stage occured at3-4day after flowering, while the free nuclei stage of Yangmail9occured at0-4day after flowering, and the cellularization stage occured at5-6day after flowering. The growth of starch endosperm cell presented S-curve and the fastest growth rate occurred between16-20d after flowering. The starch endosperm cell was polyhedron shaped and there were two kinds of amyloplasts in it, the large amyloplast was ellipsoid-or prebble-shaped, and the small amyloplast was spherical-shaped. The proliferation and growth of large amyloplasts occurred between4-16day after flowering. The small amyloplast appeared in large numbers at16day after flowering and then gradual increased in numbers. At late stage, the number of small amyloplasts accounted for more than90%of the total amyloplast in starch endosperm cell. The size of starch endosperm cell and the number of large and small amyloplasts in two wheat cultivars were Zhengmai9023>Yangmai19.(3) In wheat caryopsis, the nutrients transported from main vascular bundles into endosperm cavity. Most of nutrients directly transported from endosperm transfer cell into abdomen starch endosperm cell. While a few of nutrients transported along with the pericarp apoplast space, then through the aleurone layer and unloaded into starch endosperm cell. The nutrients in abdomen and back of caryopsis had short transportation way, and supplied preferentially in those position that leaded the starch endosperm cells highly enriched. While the nutrients in central part of caryopsis had long transportation way and the nutrients supplied much latter that made the starch endosperm cells lower enriched.2The caryopses growth and endosperm cell development in maize(1)The pigments accumulated in maize pericarp made the pericarp white or yellowish white. With the developmental days increased, the length and width of caryopsis increased and changed slowly at30day after pollination. The thickness change of caryopsis presented as unimodal curve and reached highest at24day after pollination. The fresh and dry weight changes of caryopsis presented S-curve with the highest increase rate were between6-27and9-33day after pollination, respectively. The moisture content of caryopsis was at80%-90%before12day after pollination and then gradually decreased. The grain size, weight and moisture content in two cultivars were Nongle988>Yangnuol.(2) The free nuclei stage of maize endosperm was at0-2day after pollination while the cellularization stage was at3-5day after pollination. The endosperm cell started to differentiate after6day of pollination, amyloplasts and protein bodies appeared in starch endosperm cell. The starch gradually accumulated from apex to base and from external to central in caryopsis. Amyloplasts in surrounding edge of starch endosperm filled well and the endosperm arrived as keratose, while in center starch endosperm filled poorly thus made the endosperm farinaceous. The endosperm in Yangnuol developed early and inactivated late, endosperm was highly enriched and in solid texture. While Nongle988endosperm development was lagged and inactivated early, endosperm was badly enriched and formed a cavity in the central of endosperm.(3) The nutrients transported from the base vascular bundle into placenta-chalazal region in maize caryopsis, then, most of nutrients directly transported from endosperm transfer cell into starch endosperm cell and embryo. While a few of nutrients transported along with the apoplastic space, which formed from degradation nucellus, then through the aleurone layer and unloaded into starch endosperm cell and embryo. The base and surface layer of starch endosperm cell preferential got nutrients and highly enriched, which formed keratose endosperm. The central parts of starch endosperm cells were away from surface and hardly to get the nutrients, the cells were poorly enriched and formed farinaceous endosperm.