SUCROSE TRANSPORT AND ACCUMULATION IN PARENCHYMA CELLS OF CANE STEMS: PHYSIOLOGICAL AND MOLECULAR MECHANISMS

摘要

An understanding of physiological and molecular mechanisms of sucrose accumulation is most critical to achieving high sugar levels in sugarcane. This laboratory has focussed on the subject for nearly two decades and some of the recent findings form the subject matter of this paper. Twenty-nine interspecific hybrids of a cross between S. officinarum 'Gungera' (a high sucrose clone) and S. spontaneum 'SES603' (a low sucrose clone) were raised at the experimental fields. Sucrose content of parents and their interspecific hybrids was studied by anthrone method, as well as, by brix and polarimetry. Rate of photosynthesis and translocation of sucrose from leaves down to parenchymal cells was studied using radioactive labelled NaH-~(14)CO_3. High sucrose genotypes have high radioactive counts, as compared to low sucrose types and the counts decreased as the translocation of sucrose reaches the stem parenchymal cells, being maximum in leaf midribs and least in lower internodes. Photosynthetic rates were measured also by Infra Red Gas Analysis. The activity of acid invertases in leaves and internodes were studied and it was observed that low sucrose genotypes have high acid invertases activity as compared to high sucrose genotypes. On this basis, ISH-1, ISH-5, ISH-17 and ISH-23 were graded as high sucrose and ISH-10, ISH-11, ISH-12 and ISH-25 as low sucrose. Partial protein purification of high sugar commercial cultivar COJ-64 showed a single peak in unbound fraction showing neutral invertase activity and the bound fractions showing two strong and two weak peaks giving only acid invertases activity. Activities of sucrose phosphate synthase (SPS) and sucrose synthase (SS), two other important enzymes of sucrose metabolism were also studied. These findings together with our earlier work reveal important insights into mechanism of sucrose accumulation in sugarcane.