G. F. Israelstam's research while affiliated with University of Toronto and other places

Uptake and loss of irorganic phosphate was determined in sweet potato slices ‘aged’ in the presence or absence of gibberellic acid. Concentrations of uptake medium were varied from 0.1 to 1.2 mM. Slices, aged in gibberellic acid, took up considerably less phosphate, at all concentrations than control, whereas efflux from GA3 treated discs was greater than control. Whether treated or untreated, kinetics proved to be biphasic hyperbolas. The results suggested an alteration in membrane permeability induced by gibberellic acid.

The level of gibberellin-like substances was determined in the cotyledons and axis of developing seedlings of dwarf (Little Marvel) and normal (Tall Telephone) cultivars of pea (Pisum sativum L.). The effect of cotyledon removal with GA3 application on growth was also examined. Greater levels of gibberellin-like substances were observed in the cotyledons of the normal cultivar than the dwarf. This was particularly evident in the cotyledons during the early stages of seedling growth. Subsequently there was a decline in GA levels in the cotyledons. This was coincidental with a rise in GA content in the axis with markedly greater levels in the normal than the dwarf cultivar. Decotyledonated dwarf and normal plants supplied with GA were much taller than the decotyledonated controls. This observation along with those of the gibberellin levels in the cotyledons and axis, provided circumstantial evidence that there may be translocation of gibberellins from the cotyledons to the axis.

Uptake of inorganic phosphate was determined in freshly cut and «aged» discs of Sweet potato. «Ageing» was carried out for varying time periods in the presence and absence of gibberellic acid. No difference in uptake rates were observed over the first ten hours of «ageing». Subsequently discs «aged» in the presence of gibberellic acid were found to take up considerably less phosphate than the control. No difference in respiratory rates between the treated and the untreated discs was observed. The results suggest an alteration in membrane permeability induced by gibberellic acid.

It has been observed that GA3 treatment of dwarf peas results in a decrease in photorespiratory levels in excised leaflets, and that leaflets of normal peas show lower levels of photorespiration than their dwarf counterparts. It has been suggested that this decrease in CO2 release in the light induced by GA3 may account for recorded increases in net photosynthesis when plants are treated with GA3 and that this phytohormone may be involved in a CO2 conservation system.

A simple, rapid method requiring few manipulations for the extraction of chlorophylls from fragmented leaf tissue of angiosperms and gymnosperms is compared with the widely used acetone method. Unlike the acetone method where grinding and subsequent centrifugation are essential, this method makes use of incubation at 65 °C of leaf tissue immersed in dimethyl sulphoxide. The new method was found to be as efficient as acetone for chlorophyll extraction and superior in terms of chlorophyll stability.

Levels of ferricyanide reduction, cyclic and non-cyclic photophosphorylation were measured in chloroplasts of two cultivars of pea and a comparison of their P/2e+ ratios were made. No differences were observed in cyclic photophosphorylation or ferricyanide reduction but non-cyclic photophosphorylation was lower in chloroplasts from the dwarf than the normal cultivar. Thus the P/2e+ ratio of the dwarf was lower than the normal. Dwarf seedlings treated with gibberellic acid (GA3) had similar rates of cyclic photophosphorylation as the untreated dwarf but non-cyclic photophosphorylation was lower as was ferricyanide reduction. This resulted in P/2e+ ratios that were higher in chloroplasts from the GA3 treated dwarf seedlings than the untreated, and were the same as the untreated normal. Addition of GA3 directly to the chloroplasts did not alter the activity in any way. Hence gibberellins do not directly affect changes in chloroplastic activity but may conceivably be involved in a feed-back control system.

An asparagine synthetase which is active with either glutamine or NH 4+has been found in maize (Zea mays L.) roots. Unlike the enzyme obtained from legume cotyledons, the maize-root enzyme is only slightly more efficient with glutamine (Km, 1.0 mM) than with NH 4+(Km, 2.0–3.0 mM). The activity of this enzyme is higher in the mature root than in the root-tip region, i.e. root cells develop a capacity to make asparagine from glutamine or NH 4+as they mature. β-Cyanoalanine synthetase is also present in maize roots. The apparent Km for cysteine is 2.6 mM and for cyanide is 0.57 mM. The enzyme is more active in the root tip than in mature root tissue. Thus, if asparagine were made in the root tip, the cyanide pathway could represent the mechanism of synthesis. It is our contention, however, that this potential is not realized under normal conditions because 14C-experiments performed previously have indicated a limited availability of both CN and cysteine in the maize root.

The in vivo and in vitro activity of alcohol dehydrogenase from baker's yeast maintained under aerobic and anaerobic conditions was measured. In vivo measurements were made in cells "permeabilised" with toluene. Michaelis constants (NAD+ as substrate) were found to be almost identical as those reported for purified preparations. In addition the Km of the enzyme from cells incubated under anaerobic conditions was virtually identical to that from cells from aerobic conditions. The activity of the enzyme was found to be greater (in both "permeabilised" cells and extracts) in cells maintained under nitrogen than air. Cells metabolizing glucose in N2 produced greater levels of ethanol than in air and the rate of NAD+ reduction was also found to be greater in N2 than in air. The results indicate that it was feasible to determine rates of this enzyme in vivo and that the difference in activity of alcohol dehydrogenase under N2 and air may conceivably account for differences in rates of glucose utilisation, ethanol production and NAD+ reduction in air and nitrogen.

A pyridine nucleotide transhydrogenase which could facilitate the transfer of hydrogen between chloroplastic and non-chloroplastic pools of pyridine nucleotides was isolated from the unicellular green alga Chlorella. The kinetics of this enzyme with respect to the substrate NADPH demonstrated sigmoid characteristics and substrate inhibition.

Using a sensitive fluorometric method the activity of alkaline phosphatase (E.C. 3.1.3.1) and acid phosphatase (E.G. 3.1.3.2), orthophosphoric monoester phosphohydrolase, was measured in the whole seed, de-embryonated cotyledons, embryos and in the incubation medium of dwarf (Little Marvel) and Normal (Tall Telephone) cultivars of Pea (Pisum sativum L.) over a 48 hour incubation period. Levels of gibberellin-like substances were also determined in the cotyledons and embryos of imbibed seeds. No alkaline phosphatase was found to be present. Acid phosphatase was found to be present in the dry seed and its level was found to increase quite markedly during imbibition. Levels in the dwarf cultivar increased to a greater extent than in the tall cultivar. A small amount of acid phosphatase was also found in the incubation medium — more from the dwarf than the tall, but their rate of increase was equal. Greater activity was found in both the de-embryonated cotyledons and in the embryo of the dwarf than the tall. In both cultivars, incubated cotyledons devoid of embryos showed less phosphatase activity than cotyledons from intact seeds. Addition of gibberellic acid to the incubation medium did not restore the activity lost by removing the embryonic axis. At concentrations greater than 1 µM GA3, phosphatase activity in de-embryonated cotyledons of the dwarf cultivar was considerably less than in the absence of GA3 or in cotyledons from intact seeds. Removal of the testa subsequent to imbibition but prior to incubation of the seeds, resulted in a greater activity of the enzyme, both from the cotyledons and in the incubation medium. Greater levels of gibberellin-like substances were found in the cotyledons and embryos of the normal cultivar than the dwarf. It was suggested that Gibberellins may possibly inhibit the production or activity of the enzyme acid phosphatase in Pea.