Studies On Cytology, Physiology And Biochemistry Of Floral Sex Differentiation In Litchi (Litchi Chinensis Sonn.)

Cytological, physiological and biochemical basis of sex differentiation and development of litchi were investigated. The main results are summarized as follows:1. Cell ultrastructure of litchi meristem of stem apex during the stage of transformation from vegetative growth to reproductive growth was observed using transmission electron microscope. Cells before paniculiform development were arranged tightly without cell gap. The cytoplasm was thick, vacuole was small, and most space of cell was occupied by big and round nucleus. There were abundant mitochondria and many membranaceous structures in the cytoplasm. The whole membranceous system connected nucleus inside to plasmodesmata outside. A lot of vesicles formed, fused and migrated. The results show that structure substances of cells were experiencing active synthetic metabolism and changing to accumulate enough information and substances for radical changes in the process of development. When the growth cone changed from sharp and long to thin and flat during paniculiform development, changes taken place in cellular structure to fit for the differentiation of floral primodia. The most obvious characteristics was that programmed cell death (PCD) occurred in some cells. During the PCD, condensation of nucleus, marginalization of chromatin, nuclear membrane shrinkage and destruction apparently occurred, and many vesicles appeared in the cytoplasm, which may be related to the degradation of cell substances. The degradation products were transfered to nearby cells in the form of vesicles through plasmodesmata. Therefore, the normaldevelopment of other cells and the need of other normal cell development for substances and energy were assured.2 Comparing and analyzing the dynamic changes of cellular histochemistry on litchi pistil and stamen development indicate that the accumulation of starch and protein happened in the early stage both pistil and stamen floral primordium . After meiosis, fertile pistil and stamen always keep strong PAS reaction and protein metabolism until maturity. However, abortive pistil and stamen accumulate less starch and protein. Tapetum of abortive anther does not degrade after meiosis and resulted in pollen sterility. Ultra-structure changes of anther abortion and pistil abortion during development of litchi flower indicate that the programmed cell death (PCD) also occurred in the abortive anther or pistil tissue after meiosis, which leads to weak competition ability for nutrient and gradually causes abortion of the anther or pistil.3 By comparing and analyzing the dynamic changes of carbonitride in the floral sex determination of litchi we found that: higher C/N and lower amino acid content are beneficial to androecium differentiation; in contrast, lower C/N and higher amino acid content are adequate for gynoecium differentiation; the amino acid content in androecium is only half of that in gynoecium. Proline is associated with pollen developmental capacity.4 Results obtained by analyzing the dynamic changes of polyamine, nucleic acid and proteins in differentiation process of litchi floral bud indicate that in the process from the leaf bud to the primary panicle development, the content of polyamine continually rises and reaches the peak value before the mass-synthesis of nucleic acid and proteins. So polyamine may affect floral development by regulating the synthesis of biological macromolecule. The content of Spm, Spd and soluble proteins in the mature autumn top leaf increase along with the increase of terminal buds or floral buds. It showed that the metabolism of nitrogenous compound in the leaf is vital for stern apex shiftingfrom nutritive growth to reproductive growth.Development of litchi stamen is related closely to the synthesize of Put, and development of pistil is related to high content of Spd+Spm. During development of litchi pistil and stamen, polyamine help to regulate nuclear acid and protein metabolism, which implied that polyamine has a role in regulating sex...