Abstract
Chromosome studies and soluble protein profiles, fractionated by reducing and non-reducing SDS-PAGE, were carried out in dioecious Trichosanthes bracteata. Somatic chromosome no. 2n = 22 was recorded in both sexes. The karyotype of male and female plant shows high homogeneity and the absence of any heteromorphic pair of chromosomes negates the possibility of XY mechanism. Soluble protein profiles from the tuberous roots of the male and female plants, fractionated by reducing SDS-PAGE, did not show any qualitative distinction. Whereas the protein profile in non-reducing SDS-PAGE reveals a clear distinction when compared on a single gel. The difference is marked by the presence of a disulphide linked tertiary or folded protein at 19 k D region detected in male sex. However, at the level of primary structure the qualitative expression is similar indicating a common ancestry.
Highlights
Most of the flowering plants are bisexual having flowers with both male and female reproductive organs and only less 4% plant species are dioecious in nature i.e., strictly maintain their sexual phenotypes [1]
Chromosomes are short to medium in size and could be classified [19] into 4 distinct morphological types: Type A: Short chromosomes (1.68 μm) bear 2 constrictions, primary and secondary, one is nearly sub-median and the other is sub-terminal in position; Type B: Chromosomes are short (2.13 μm) having 2 constrictions, primary and secondary, both are nearly sub-median in position; Type C: Short chromosomes (1.06 μm - 1.60 μm), the constriction of chromosomes are median and or nearly median in position; Type D: The chromosomes (2.96 μm) are medium in size and the constrictions are nearly sub-terminal in position
The karyotype of male and female plants exhibits a gross similarity in the types of chromosome present, number of chromosomes with secondary constriction, TF%, chromosome arm symmetry index and total chromosome length (Table 1)
Summary
Most of the flowering plants are bisexual having flowers with both male and female reproductive organs and only less 4% plant species are dioecious in nature i.e., strictly maintain their sexual phenotypes [1]. The vast majority of the dioecious plant species have no visibly different sex chromosomes and only some species show distinct X and Y chromosomes in relation to sex [2,3,4,5]. Chromosomal sex determination system in flowering plants indicates that the plant sex chromosomes have evolved recently through replicated independent events [6]. Trichosanthes bracteata (Lamk.) Voigt, a vegetatively propagated dioecious perennial species of cucurbitaceae, commonly grows in moist thickets and is distributed in the Eastern Himalayas in India, Bangladesh, Southern China, Southern Japan, Malayasia and tropical Australia [7,8]. The seeds of T. bracteata contains high amount of punicic acid [10]
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