Responses of Pea and Triticale Photosynthesis and Growth to Long-wave UV-B Radiation

Pea plants were more susceptible to long-wave UV-B irradiation (305 – 320 nm, 7.7 kJ m^–2 d^–1, 4 weeks) in comparison with the triticale. This difference was more apparent from the changes in total area of leaves and dry mass of shoots, rather than from the parameters of chlorophyll fluorescence and net photosynthetic rate.     

Effect of Radiation Quality on Growth and Photosynthesis of Acacia mangium Seedlings

Radiation quality was an important environmental cue to stimulate seed germination in Acacia mangium. The photo-synthetic CO₂ assimilation rate, dark respiration rate, total biomass, and relative growth rate of seedlings grown under monochromatic radiation were significantly lower than those of seedlings grown under full spectrum radiation. Blue and red radiation induced shade-avoidance and shade-tolerant responses of A. mangium seedlings, respectively.     

New Plant Growth Regulators Protect Photosynthesis and Enhance Growth Under Drought of Jack Pine Seedlings

To determine whether natural plant growth regulators (PGRs) can enhance drought tolerance and the competitive ability of transplanted seedlings, 1.5-year-old jack pine (Pinus banksana Lamb.) seedlings were treated with homobrassinolide, salicylic acid, and two polyamines, spermine and spermidine, triacontanol, abscisic acid (ABA), and the synthetic antioxidant, Ambiol. PGRs were fed into the xylem for 7 days and plants were droughted by withholding water for 12 days. ABA, Ambiol, spermidine, and spermine at a concentration of 10 μg L⁻¹ stimulated elongation growth under drought, whereas ABA, Ambiol, and spermidine maintained higher photosynthetic rates, higher water use efficiency, and lower Ci/Ca ratio under drought compared with control plants. The damaging effects of drought on membrane leakage was reversed by Ambiol, ABA, triacontanol, spermidine, and spermine. Because ABA, Ambiol, and both polyamines enhanced elongation growth and also reduced membrane damage in jack pine under drought, they show promise as treatments to harden seedlings against environmental stress. The protective action of these compounds on membrane integrity was associated with an inhibition of ethylene evolution, with a reduction in transpiration rate and an enhancement of photosynthesis, which together increased water use efficiency under drought. Although most of the tested compounds acted as antitranspirants, the inhibition in membrane leakage in ABA-, Ambiol-, and polyamine-treated plants appeared more closely related to the antiethylene action. Received December 30, 1998; accepted October 14, 1999     

Effects of Some Growth Regulators on Polyamine Biosynthetic Enzymes in Etiolated Pea Seedlings

This study was designed to examine possible links between polyaminebiosynthesis and effects of growth regulatory compounds. Anauxin (IAA), a cytokinin [benzyladenine; benzylaminopurine (BAP)],an ethylene source (ethephon) and abscisic acid (ABA) were individuallyapplied to terminal buds of excised etiolated or red light (R)-exposedpea epicotyls. Effects were noted on bud fresh weight and onthe two main enzymes of putrescine biosynthesis, arginine decarboxylase(ADC; EC 4.1.1.19[EC]) and ornithine decarboxylase (ODC; EC 4.1.1.17[EC]).As previously reported [Dai and Galston (1981) Plant Physiol.67: 266], both bud growth and ADC activity are increased byR light. In such buds, ADC is raised further by 1–10 µMBAP or ABA and inhibited by 1–10 µM IAA or ethylene(50 mg/liter or more of ethephon). In all cases, effects ofR-irradiation plus 1 mM growth regulators on ODC activity wasthe inverse of their effects on ADC, indicating independentcontrol of these pathways. These results do not support theview that putrescine biosynthetic activity is correlated withgrowth in etiolated pea seedlings. ¹Supported by a grant from NSF to A.W.G.²Supported by a grant from the Turkish Government. Permanentaddress: Department of General Botany, University of Istanbul,S?leymaniye, Istanbul, Turkey.³On sabbatical leave from the Department of Horticulture, HebrewUniversity of Jerusalem, Rehovot, Israel. (Received September 22, 1983; Accepted February 28, 1984)     

Temperature and Anoxic Injury in Pea Seedlings

Anaerobic incubation of newly germinated pea seedlings understerile conditions on moist filter paper was used to distinguishbetween the physical effects of excess moisture on soaking injuryand the metabolic consequences of prolonged anoxia. Over a 4d incubation period seedling death after anoxia fell as temperaturewas reduced from 25 to 5 °C. Internal ethanol concentrationsincreased with length of anaerobic incubation but fell withdecrease in temperature. For all combinations of temperaturewith length of anaerobic incubation, seedling survival was alwaysinversely related to ethanol concentration. An internal ethanolconcentration of 60 µM appeared to be a threshold valuefor seedling survival as anoxic death occurred only when thisconcentration was exceeded.     

Control of Leaf and Stem Growth in Light-grown Pea Seedlings by Two High Irradiance Responses

The control exerted by light on leaf and stem growth in light-grown Alaska pea seedlings was studied during the main photoperiod. Two high irradiance responses were observed. The action spectrum for one had a single sharp peak at 600 nanometers. The action spectrum for the other showed a broad peak between 440 and 470 nanometers. These two light responses must be activated simultaneously for any inhibition of stem growth or promotion of leaf growth. Both action spectra may be explained in terms of the high irradiance response of phytochrome.     

Dry-matter Production and Photosynthesis in Pine Seedlings

Growth analysis and photosynthesis measurements were carriedout on first-year seedlings of Pinus radiata, P. contorta, andP. nigra. P. sylvestris was also included in two growth-analysisexperiments. There appeared to be no difference in relativegrowth-rate (RGR) between the species mentioned, except betweenP. radiata and P. nigra. It was found that when the level ofmineral nutrition was high, P. radiata had a higher RGR thanP. nigra and that the reverse was true at low mineral nutrientlevels. There was no difference in net assimilation rate (NAR)between the species, but NAR appeared to increase and decreasewith mineral nutrient supply. Net photosynthesis per unit of leaf was somewhat higher in P.radiata than in P. contorta; P. nigra had a lower photosyntheticrate than either P. radiata or P. contorta.     

The Metabolism of Ethanol in Germinating Pea Seedlings

Considerable losses of ethanol occurred during the germinationof green pea seeds which could not be ascribed to losses dueto the volatility of the alcohol. Changes in the contents ofacetaldehyde, acetone, organic acids, and in the gas exchangessuggested that the alcohol was oxidatively metabolized. Feedingethanol to slices of pea cotyledon tissue also indicated ethanolconversion to acetaldehyde and the interconversion of acetaldehydeand acetone. Feeding ethanol 2:¹⁴C to the slices confirmed thatthe ethanol was metabolized, giving similar changes in the contentof carbonyl compounds and organic acids to those observed inthe intact germinating pea seedlings. Thus the endogenous ethanolwhich accumulated when pea seed imbibed water prior to germinationmay be metabolized subsequently by the germinating seedling.     

The Stability and Movement of Gibberellic Acid in Pea Seedlings

The stability and movement of gibberellic acid (GA) in intactdwarf pea seedlings growing in the light was studied by meansof both unlabelled GA and GA labelled with isotopic carbon (¹⁴C).After ¹⁴C-GA had been applied to the mature leaves of pea seedlingsmuch remained in association with the treated leaflets, but¹⁴C-GA was also extractable from the young shoots. The yieldwas approximately the same 5 to 96 hours after treatment. GApenetrated leaf surfaces only while the application solventwas moist (about 1 hour), but moved from the treated leafletsinto the shoots for at least 24 hours. Some hours after treatmentthere was an abrupt increase in the growth-rates of the plants,and crude estimates suggest that an effective dose of GA movedto the elongating tissue at about 5 cm/hr. The pattern of distributionof ¹⁴C was examined by autoradiography. The data suggest thatGA which enters the plant is redistributed from maturing leavesto immature leaves, passing through the elongating tissue, foras long as any of the substance is present. The hypothesis remainstenable that GA produces its growth effects by acting only uponexpanding tissue     

The Krebs Cycle Enzyme System of Pea Seedlings

A particulate fraction, showing catalytic activity towards intermediatesof the Krebs cycle, has been isolated from pea seedlings bythe method of differential centrifugation. The particulate material,possibly consisting of mitochondria, appears homogeneous underthe microscope and is stained by Janus Green B. The enzyme system necessary for the integrated and single stepreactions of the Krebs tricarboxylic acid cycle is described,and the requirenients for cofactors, discussed.     

Some Characteristics of Formyltetrahydrofolate Synthetase from Pea Seedlings

It has been found, that ammonium sulfate is effective not only in stabilizing, but also in stimulating the activity of formyltetrahydrofolate synthetase (E. C. 6, 3. 4. 3) purified approximately 500-fold from pea seedlings. Kinetic studies have indicated that the stimulation by ammonium sulfate is due to the enhancement of the binding of the substrate, formate, with the enzyme. The binding of the another substrate, FAH₄, with the enzyme was not affected by the addition of ammonium sulfate. The enzyme activity was inhibited by various sulfhydryl reagents, and the inhibition by PCMB was overcome by the addition of l-cysteine. The inhibition by PCMB was competitive with FAH₄, and the K_i value for PCMB was 0.8 × 10?⁶m.     

Kinetin Supplementation Modifies Chromium (VI) Induced Alterations in Growth and Ammonium Assimilation in Pea Seedlings

In the present study, impact of kinetin (KN; 10 and 100 μM) supplementation on growth, ammonium (NH(4)(+)) assimilation and antioxidant system in pea under hexavalent chromium toxicity (Cr VI; 50, 100 and 250 μM) was investigated. Chromium decreased growth, protein, and nitrogen, and activity of glutamine synthetase (GS) and glutamate synthase (GOGAT) while it increased NH(4)(+) content and activity of glutamate dehydrogenase (GDH). Kinetin at 100 μM decreased growth and NH(4)(+) assimilation, and together with Cr, it increased Cr toxicity. Chromium and 100 μM KN increased superoxide dismutase (SOD) and ascorbate peroxidase (APX) activities while decreasing activities of catalase (CAT), glutathione reductase (GR) and dehydroascorbate reductase (DHAR). Ascorbate and glutathione levels were decreased by Cr and 100 μM KN. In contrast, supplementation of 10 μM KN under Cr (VI) toxicity, protected NH(4)(+) assimilation and promoted growth of pea by increasing levels of some of the antioxidants i.e., CAT, GR, DHAR, ascorbate and glutathione. Results showed that 10 μM KN increases Cr tolerance while 100 μM KN exhibited opposite responses. These results could contribute to an understanding of the mechanisms of KN-mediated dual influence on metal tolerance in crop plants.