Cucumber Sex Differentiation

Cucumber is a unique model plant for sex expression. Studies on sex differentiation of cucumber has both practical and theoretical significance. The mechanism of sex differentiation and expression in cucumber was investigated using the androecious line (ZH-20)and full female line (GYl)as material in our study..Morphological analyses were conducted on differentiation and development of female and male sex organs during the floral bud initiation and sex differentiation process in cucumber, and the results showed that the development of female and male flowers could be divided into 10 stages, and the formation of cucumber unisexual flowers first underwent a hermaphoroditic stage, then developed forward maleness or femaleness. No significant morphological difference existed hi female and male flowers at stages earlier than hermaphoroditic stage (stage 5), after which the flower bud developed unisexually. The center of female floral bud is concave, then the hypogynous ovary appeared and the unisexual female flower was formed finally; while the anther of male floral bud enlarged rapidly and the unisexual male flower was formed finally.Development of carpel in cucumber male flower was studied by morphological, histochemical and isoenzyme electrophoretic analysis. The results showed that: (1) cell number of the carpel in male flowers increased continuously during the development of male flower, and the carpel in male flowers was abundant in RNA content; (2) the carpel in male flower at latter developmental stage was differentiated, and a placenta-like structure was formed in the carpel of male flower during anthesis, while ovule did not appear as that of mature female flower; (3) The POD and esterase isoenzyme electrophoretic profile of carpel varied with the development of male flower and SDS-PAGE analysis of carpel indicated that the carpel in male flowers at latter development stages could synthesize new proteins, which furtherindicated that the carpel in mature male flower was no longer at the stage of primordium. It could be deduced from the results that carpel of cucumber male flowers develops continuously in a distinct pattern with that of female flowers during sex expression process.A partial cDNA fragment of cucumber spermidine synthase gene was isolated by RT-PCR, and the full-length cDNA was obtained by 5 -RACE and 3 -RACE techniques. Sequences analysis showed that the size of full-length cDNA was 1398 bp which contains a 951 bp coding region encoding 317 amino acid residues. CsSPDS amino acid sequences showed high degree identity compared with known SPDS from other species. And SPDS from Coffea arabica has the highest similarity to CsSPDS. Organ-specific expression analysis indicated that the CsSPDS gene expression was predominant in rapid growing tissues such as young roots, flower buds and young leaves. The response of CsSPDS expression to the sex reversal from male to female by the application of ethephon to seedlings at 3 leaf stage was also examined, and the results showed that the CsSPDS transcript level in shoot apices decreased 2h after treatment, increased 4h after treatment, reached the peak 8h after treatment, and the CsSPDS transcript level of treatment was always higher than that of control. The relationship between ethylene and polyamine metabolism and its role in sex expression of cucumber were also discussed.