Correlative Influence of Axes on Senescence of Cotyledons Following Germination of Mung Bean Vigna Radiata (L.) Wilczek Seeds

Immediately after seed germination cotyledons undergo transient development culminating in senescence, which is different from that of a leaf. In the present study senescence of mung bean (Vigna radiata) cotyledons following germination has been characterized to understand correlative influence of axes. Cotyledons isolated from axes showed retardation of storage protein degradation as well as increased chlorophyll synthesis followed by senescenceinduced decline. When one of the pair of cotyledons was detached from the axis, the attached cotyledon showed same characters like intact cotyledons but the detached one showed the behavior similar to the isolated cotyledons. When epicotyls were removed after 3 days incubation cotyledons remained attached with axes for longer period and decline in chlorophyll content retarded compared to control, but decline in protein level remained unaffected. Removal of root tip marginally delayed the decline in both chlorophyll and protein level. Morphological studies also showed maintenance of greenness and fullness of cotyledons when isolated or epicotyls removed. Histological studies revealed that storage bodies started degenerating following germination from the peripheral zone while chloroplast development progressed around vascular bundle ending with signs of senescence in the last phase. Both storage body degeneration and chloroplastic senescence was delayed in case of isolated cotyledons. Therefore, cotyledons in case of epigeous germination of seeds pass through complex developmental changes. Immediately after germination storage mobilization starts from the periphery to provide soluble substrates to growing axes along with photosynthetic development around vascular bundle; the latter ends with senescence-induced degeneration influenced by emerging epicotyl acting possibly as sink.