NEET BIOLOGY

Detailed explanation-1: -The plant hormone that results in the abscission of leaves, senescence, bud dormancy and inhibition of cell division is ABA or abscisic acid. Therefore, the correct option is option D.

Detailed explanation-2: -Many studies have shown that exogenous abscisic acid (ABA) promotes leaf abscission and senescence.

Detailed explanation-3: -Ethylene and Auxin In particular, leaf abscission is under the control of auxin and ethylene. Burg (1968) suggested that ethylene caused leaf abscission in vivo by inhibiting auxin synthesis and transport or enhancing auxin degradation, thus, lowering diffusible auxin level.

Detailed explanation-4: -ABA is a key hormone that regulates water status and stomatal movement. Under drought conditions, plants produce and accumulate increased amounts of ABA in the guard cells, and this induces stomatal closure to conserve water.

Detailed explanation-5: -Previous studies have suggested that ABA induces senescence by increasing biosynthesis of ethylene. However, a recent study has revealed that ABA also induces senescence through core ABA signaling in an ethylene-independent way (Zhao et al. 2016). During leaf senescence, senescence-associated genes (SAGs) are induced.