Proline Metablism During Water Stress in Mulberry

The influence of water stress on proline metabolism was studiedin 3-month-old mulberry plants at four levels of water stress.Leaf water potential was drastically decreased in all treatments.Though leaf area and relative water content were decreased,drastic decrease was observed only in very severe stress treatments.Proline accumulation was observed both in roots and leaves instress treatments; but accumulation was greater in roots thanin leaves. The enzymes, proline dehydrogenase and proline oxidase,were inhibited under stress conditions. Proline oxidase wasmore inhibited in roots than in leaves. The significance ofthe relative activities of these two enzymes is discussed. Key words: Water stress, proline dehydrogenase, proline oxidase     

Intrachloroplast Localization of 65Zn and 63Ni in a Zn-tolerant Plant, Ocimum basilicum Benth

Intrachloroplast localization studies of ⁶⁵Zn and ⁶³Ni weremade in a Zn-tolerant plant Ocimum basilicum var. purpurascensBenth. in order to investigate the mechanism and specificityof metal tolerance. The isotopes were supplied in solution tothe roots 14 d before fractionation. It was observed that ⁶⁵Znactivity was comparatively greater in the chloroplast envelopemembranes and stroma than the ⁶³Ni; and ⁶³Ni was largely foundin the lamellar and stroma fractions. Further analysis of lamellaerevealed that photosystem II (PS II) particles were richer inradioactivity than photosystem I (PS I) particles. The photochemicalevents of photosynthesis were less affected in Zn-treated plantsthan in the Ni-treated plants. The changed levels of the electrontransport chain intermediates including cytochromes, plastocyaninand ferredoxin provide supporting evidence for the localizationstudies. The activity of carbonic anhydrase, a zinc metalloprotein,was increased in Zn-treated plants with increase in nutrientZn concentration, indicating the binding of zinc to a proteinmoiety in the chloroplasts.     

Photo-Acoustic Spectroscopy of Pubescent Leaves

The optical absorption spectra of pubescent (hairy) and depubescisedleaves of Blumea oxydonta DC and Gomphrena decumbens Jacq weretaken using the relatively new technique of photo-acoustic spectroscopy.The pubescent leaf gave a higher photo-acoustic intensity thanthe depubescised leaf. The adaptive significance of pubescenceto the leaf is discussed. Key words: Photo-acoustic spcctroscopy, pubescence     

Sites of action of sulphite and bisulphite in the photosynthetic apparatus of sugar maple leaves as studied by photo-acoustic and modulated fluorescence methods

The photosynthetic activity of intact sugar maple leaves has been assessed in the presence of exogenous sulphite, bisulphite and sulphate under varying light conditions using photo-acoustic and modulated fluorescence methods. In the light, bisulphite was found to be more toxic than the other two, sulphate being the least toxic of all. Interestingly, the vitality index, R_rd, measured as the ratio of the modulated fluorescence decrease (F_d) to the steady-state fluorescence (F_s), which indicates the efficiency of the whole photosynthetic activity, was more affected than the total photosynthetic energy storage (PES) of PSII and PSI during linear and cyclic electron transport, and F_v/F_m (PSII activity). The severity of the damage appeared to be a function of light intensity. Bisulphite treatment in darkness resulted in a dramatic decrease in R_rd, a moderate decrease in PES and a marginal decrease in F_v/F_m. As for sulphite, the effect was negligible with a tendency for enhanced activity. It is inferred that the Calvin cycle is a good candidate for the primary site of bisulphite and sulphite action. Recovery of activity, especially at the R_rd level, obtained in the presence of ascorbate, glutathione and L-cysteine, indicated a contribution of O₂ free radicals to the observed inhibition of the photosynthetic activity in the light.     

Photoacoustic Spectroscopy--Leaf Absorption Spectra

Using a relatively recent technique, photoacoustic spectroscopy(PAS), purple pigmentation in leaves of three species of Euphorbiawas characterized as anthocyanin by observing a peak at 545nm. The in vivo chlorophylls of the leaf have a recorded maximumabsorption peak at 675 nm as against 665 nm of the in vitrochlorophylls. The intensity of purple pigmentation in leavesof Euphorbia hirta L., are inversely correlated to the soilmoisture levels, leaf water content and leaf water potentials.The applicability of PAS to biological samples was discussed.