Auxin, Cytokinin and Ethylene Differentially Regulate Specific Developmental States Associated with Shoot Bud Morphogenesis in Leaf Tissues of Mangosteen (Garcinia mangostana L.) Cultured in Vitro

Hormonal regulation of de novo shoot bud formation in leaf explantsof mangosteen has been studied from a developmental perspective.This analysis indicates that at least three discrete, experimentallydistinguishable developmental states, namely, morphogenic competence,caulogenic determination and organ differentiation, were expressedduring shoot bud morphogenesis. The state of morphogenic competencein leaf tissues was expressed maximally between days 10 and12 of leaf development. Competent cells in explants requireda minimum of 6 days of BA treatment (20 µM) to becomecaulogenically determined. Such determined cells would continueshoot organogenesis on medium devoid of growth regulators. Delayingof BA exposure for as short as 2 days caused a dramatic declinein tissue competence. The state of competence and the processof caulogenic determination were adversely affected by IAA,but were insensitive to ethylene or its precursor, ACC. Shootbud differentiation was greatly enhanced by BA, but selectivelydelayed by ethylene. IAA also showed an inhibitory effect onshoot bud differentiation, but not mediated through ethylene.The distinct roles of auxin, cytokinin and ethylene on the regulationof shoot bud development in mangosteen leaf explants have beendiscussed on the basis of the current understanding of the conceptof tissue competence, determination and differentiation. (Received August 12, 1996; Accepted October 31, 1996)     

Dietary chitosan supplementation attenuates isoprenaline-induced oxidative stress in rat myocardium

Despite considerable advances in diagnosis and management over the last three decades, acute myocardial infarction continues to be a major public health problem. It is predicted that ischemic heart diseases will constitute the major disease-burden worldwide in the year 2020. In the present study, an attempt has been made to examine the effects of dietary chitosan supplementation on lipid peroxidation and cardiac antioxidant defense system in isoprenaline-induced myocardial infarction in rats, an animal model of myocardial infarction in man. Dietary chitosan intake significantly attenuated the isoprenaline-induced lipid peroxidation and maintained the level of reduced glutathione at near normal. Its administration demonstrated an antioxidant effect by maintaining the activities of myocardial glutathione dependent antioxidant enzymes (glutathione peroxidase and glutathione-S-transferase) and antiperoxidative enzymes (superoxide dismutase and catalase) at levels comparable to that of controls. The results of the present study indicate that the salubrious effects of dietary supplementation of chitosan is probably related to a counteraction of free radicals and/or to normal maintenance of the activities of free radical enzymes and the level of GSH, which protect myocardial membrane against oxidative damage by decreasing lipid peroxidation.     

Studies on the visual pigment and the indicator yellow analogues formed from 5,6-monoepoxyretinal

1. A new visual pigment has been isolated from retinae of rats maintained on 5,6-monoepoxyretinal for a period of 6 months. 2. Indicator yellow analogues from 5,6-monoepoxyretinal, namely 5,6-monoepoxyretinylidenemethylamine and 5,6-monoepoxyretinal oxime, have been prepared in a homogeneous state, the latter being obtained crystalline. 5,6-Monoepoxyretinylidenedimethylammonium iodide has also been prepared. 3. The spectroscopic properties, analytical data and antimony trichloride colour reactions of these indicator yellow analogues confirm their Schiff base structure. 4. The nature of chromogens formed from 5,6-monoepoxyretinylideneamino compounds with antimony trichloride and concentrated sulphuric acid is obscure although the chromogens resemble one another very closely. 5. 5,6-Monoepoxyretinylidenemethylamine and 5,6-monoepoxyretinylidenedimethylammonium iodide are very labile, whereas 5,6-monoepoxyretinal oxime is quite stable. 6. Hydrolysis of 5,6-monoepoxyretinylidenemethylamine as a function of pH reveals that, though 5,6-monoepoxyretinylidenemethylammonium ions are stable, the un-ionized compound readily hydrolyses to 5,6-monoepoxyretinal. This hydrolysis can be prevented by excess of un-ionized methylamine and hastened by formaldehyde. 7. The bathochromic shift in the λ_max. of the `acid form' of 5,6-monoepoxyretinylidenemethylamine is due to the formation of its ammonium salt. The spectrum of the `acid form' is identical with that of 5,6-monoepoxyretinylidenedimethylammonium iodide in ethanol. This is also evidence for the quaternary state of the nitrogen atom during the `acid shift' of 5,6-monoepoxyretinylidenemethylamine. 8. The significance of 5,6-monoepoxyretinal and the corresponding indicator yellow analogues in the formation and properties of a new visual pigment is discussed.