Zeitschrift für Pflanzenphysiologie最新文献

Tuberisation in potato is accompanied by a substantial decrease in both total and reducing sugar levels in the stolon tip. There is a negative relationship between tuber growth and the ratio of reducing sugars : sucrose. However, a positive and statistically significant correlation exists between the ratio of glucose : fructose and the degree of tuberisation as determined by fresh weight measurement. This change in metabolism is confirmed by a pulse chase study using ¹⁴CO₂.

While cytokinin-like activity was detected in aseptically cultured excised roots of Zea mays no evidence could be found that (8-¹⁴C)adenine or (U-¹⁴C)adenosine was incorporated into the biologically active compounds over a 42 day culturing period. This information raises serious doubts as to whether adenine and/or adenosine serve as primary precursors for cytokinin biosynthesis. The possibility does however, exist that the excised roots lacked a shoot produced precursor necessary for cytokinin production.

Using microaerobic conditions, stable preparations of soybean (Glycine max var. Bragg) root nodule protoplasts were isolated. The enzyme mixture consisted of 2% Cellulase R10, 1% Macerozyme R10 in a 0.6 M mannitol osmoticum.

The protoplasts showed acetylene reduction activity of up to 50nmol ethylene g^-1 nodule FWh^-1 for at least 12 hours. This activity occurred immediately after isolation, and no lag period was observed. The observed specific activities were considerably (up to 40 fold) higher than those previously reported (e.g. Schetter and Hess 1977). However, in view of the overall reduction of activity which is observed between the whole plant stage and the isolated protoplasts (about a 1000 fold decrease), one has to question the general applicability of the isolated protoplast system for the study of physiological parameters affecting symbiotic nitrogen fixation.

Shoots from four-day old light-grown pearl millet (Pennisetum americanum [L.] Leeke) seedlings, grown continuously in the presence of 1.32 × 10^-5M norflurazon (NF), lacked chlorophyll and failed to accumulate abscisic acid (ABA) when water stressed. Chlorophyll and stress-induced ABA contents were significantly correlated (r = 0.82, P<0.001) for seedling shoots treated with a range of NF concentrations.

No inhibitory effect on ABA accumulation by NF occurred if seedlings were grown at low light intensity (<20 μmol m^-2 s^-1 photosynthetic photon flux density), or if NF was applied 3 days after sowing to already greened seedlings. Neither was ABA accumulation affected by the related non-bleaching compound, SAN 9785.

The results suggest that norflurazon had no «direct» effect on ABA accumulation. The possibility that structurally and functionally intact chloroplasts are required for this process is discussed.

Heat tolerance was found to change markedly during the course of the day in the CAM plant Aeonium haworthii and the C3 plant Aichryson laxum, both Sempervivoideae from the island of Tenerife. The temperature limits of heat tolerance of A. haworthii varied between 39°C and 46.5°C, and of Aichryson laxum between 43°C and 46°C. In a 12 : 12 hours photoperiod, 10°C in dark, 25°C in light, the heat tolerance reached a minimum during the dark phase and a maximum in the light phase. This was also the case when the light-dark sequence was inverted. The heat tolerance cycle appears to be induced by photoperiod and temperature, and maximum levels related to temperature. The diurnal course of heat tolerance is almost the exact inverse of tissue acid accumulation and it appears that high acidity levels may negatively affect heat tolerance. Further investigations into the physiology of the actions of the acidity could provide new insight into the mechanism of heat tolerance.

Excised Hordeum roots were employed to examine the effect of supplying copper as a complex ion on the subsequent accumulation of copper within the roots. The uptake of copper from various complexes was compared to uptake from an inorganic salt at a series of points in time. Additionally two isomeric forms of one ligand were employed to investigate the role of absolute configuration on copper availability to the plant tissue. Finally the effect of other metal ions on uptake from both free and complexed copper sources was investigated, and it was concluded from all the evidence that uptake of copper into the plant tissue occurred as a result of absorption of the uncomplexed cupric ion.

Low molecular weight carbohydrates (LMWC) occurring in both young and old leaves of 22 mangrove species from Northern Queensland (Australia) were identified using gas liquid and gas capillary chromatography. The cyclitol, pinitol, was the most prevalent compound in all members of the Rhizophoraceae and in the mangrove fern Acrostichum speciosum. In addition, Aegialitis annulata stored chiro-inositol. Another cyclitol, quebrachitol, occurred in Excoecaria agallocha. Mannitol, a polyol, was dominating in Aegiceras corniculatum, Lumnitzera littorea, Lumnitzera racemosa, Sonneratia alba and Scyphiphora hydrophylacea. The sugars sucrose, glucose, and fructose were not generally stored in high concentrations (except Xylocarpus granatum, 300 mol · m⁻³ plant water). Those species which contained no cyclitols or mannitol were low in their LMWC content. LMWC concentrations were higher in young leaves than in old ones in nearly all species under investigation.

Polyols and cyclitols may have taxonomically associated distributions and may play a role in osmotic adjustment.

We have examined the effects of various inhibitors of glycollate metabolism on glycollate excretion, photosynthetic CO₂ assimilation and N₂ fixation by cyanobacteria. α-HPMS (α-hydroxy-α(2-pyridyl)-methane sulphonate) increased the rate of glycollate excretion by Anabaena cylindrica considerably, but also inhibited net CO₂ photoassimilation and N₂ fixation. α-HPMS inhibted glycollate dehydrogenase in A. cylindrica extracts but did not affect ribulose bisphosphate carboxylase or phosphoglycollate phosphatase activities. Diamox (5 acetamido-1,3,5-thiadizaole-S-sulphonamide) also stimulated glycollate excretion, inhibited CO₂ fixation and caused a low inhibition of N₂ fixation. INH (isonicotinic acid hydrazide) enhanced glycollate excretion by A. cylindrica, suggesting the metabolism of glycollate via the glycineserine pathway, but again inhibited CO₂ fixation and N₂ fixation. Glyoxylate also stimulated glycollate excretion by A. cylindrica, Anabaena variabilis and Nostoc muscorum. The data are discussed in terms of the specificity of glycollate metabolism inhibitors in cyanobacteria and the regulation of glycollate metabolism in these organisms.

Maize root protoplasts respond to IAA by bursting and the number of surviving protoplasts decreases with increasing IAA concentration. The disruption of the plasmalemma of protoplasts deriving from root cells pretreated by IAA is less. When protoplasts are prepared from the upper and lower parts of the extending zone of gravireacting roots, a higher number of protoplasts from the lower side «survive» in the presence of IAA. This suggests that the content of endogenous IAA of the lower cells is larger than that of the upper cells.