Translocation of 32P from leaves to seeds of sunflower and associated biochemical changes in young and mature leaves during seed-filling

Abstract

Transport of ³²P from mature leaves was studied at stage I (ray florets opening), stage II (50% florets opening) and stage III (central disc florets opening) of the capitulum in order to ascertain the capacity of developing seeds to draw metabolites. Experiments showed that when feeding was done at stage I separately in the 6th, 7th and 8th leaf from the apex, accumulation of ³²P was maximum in the peripheral seeds of the corresponding zone of the fed leaf. Also at stage II was ³²P accumulation high in the peripheral zone along with high accumulation in the inner zone. But at stage III and IV (seven days after central disc florets opening) when accumulation declined considerably in the peripheral zone, very little accumulation of ³²P was noted in the central zone of the capitulum. During maximum sink demand i.e. at stage II, the soluble cabohydrate level increased both in apically borne young and mature leaves but declined thereafter only ,in mature leaves. In both young and mature leaves the chlorophyll level, however, did not show any decline even at stage IV, It was further observed that dry matter retention capacity declined only in young leaves from stage II onwards. In young leaves, catalase activity was low from stage II whereas in mature leaves it was low at stage II followed by a transient sharp increase at stage III.