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Leaf Stage (leaf + stage)
Selected AbstractsLight gains and physiological capacity of understorey woody plants during phenological avoidance of canopy shadeFUNCTIONAL ECOLOGY, Issue 4 2005C. K. AUGSPURGER Summary 1Carbon gain during phenological avoidance of canopy shade by an understorey plant depends on the extent of avoidance, the leaf stage during avoidance, and whether young and old leaves can exploit greater light availability in spring and autumn. 2For Asimina triloba (L.) Dunal., Aesculus glabra Willd., Acer saccharum Marsh., Lindera benzoin (L.) Blume and Carpinus caroliniana Walt. in a deciduous forest in Illinois, USA, spring avoidance with leaves at full size ranged from 0 days for Asimina to 24 days for Aesculus, and brought 36,98% of estimated total annual irradiance. Autumn avoidance was non-existent to minimal in all species. 3Total chlorophyll reached maximum concentrations at the middle of leaf life span, and declined well before senescence. Leaf nitrogen concentrations and net photosynthetic capacity both peaked in youngest leaves during spring avoidance, and were low in old leaves during autumn avoidance. 4Aesculus had especially high photosynthetic capacity during precanopy closure, while Asimina had relatively low capacity in its later developing leaves. 5Young leaves of species with phenological avoidance can enhance C gain, while old leaves in autumn do not. Thus phenological avoidance in spring may enhance the persistence of understorey woody individuals of some species. [source] The effect of temperature and daylength on heading in tetraploid cultivars of rhodesgrass (Chloris gayana Kunth)GRASSLAND SCIENCE, Issue 4 2005Isao Tarumoto Abstract The present study was conducted to clarify the effect of temperature and daylength on heading in tetraploid cultivars of rhodesgrass (Chloris gayana Kunth). Five cultivars, Tochiraku-kei (2,), Fords Katambora (2,), Callide (4,), Masaba (4,) and Pokot (4,), were planted on three dates at 1-month intervals (4 May, 4 June and 4 July) in three of the Ministry of Agriculture, Forestry and Fisheries research institutions in Ishigaki (Tropical Agriculture Research Center), Nishigoshi (Kyushu National Agricultural Experiment Station) and Nishinasuno (National Grassland Research Institute) in 1978. Three tetraploid cultivars were planted on three dates at 1-month intervals (4 May, 4 June and 4 July) under four daylength-treatments of natural daylength (ND), 12 h daylength [12 h], ND/12 h and 12 h/ND, and changed daylength at the eighth leaf stage, in Nishinasuno in 1978. Under natural daylength, although heading was not observed for Masaba and Pokot, heading was observed in all plots for Tochiraku-kei, Fords Katambora and Callide, and their days to heading (DH) linearly decreased with increases in daily mean temperature (DMT). The result indicated that, under natural daylength in summer, temperature was a major factor in determining DH in tetraploid Callide, which was the same as in diploid rhodesgrass cultivars. Callide reached heading under all four daylength treatments. However, Masaba and Pokot reached heading only under 12 h and ND/12 h treatments, suggesting that Masaba and Pokot have qualitative sensitivity to photoperiods that operate after the ninth leaf stage. These findings would be useful in tetraploid rhodesgrass for estimating foliage harvesting time in the field and for conducting cross-pollination in a greenhouse during winter. [source] DROUGHT STRESS: Comparative Time Course Action of the Foliar Applied Glycinebetaine, Salicylic Acid, Nitrous Oxide, Brassinosteroids and Spermine in Improving Drought Resistance of RiceJOURNAL OF AGRONOMY AND CROP SCIENCE, Issue 5 2010M. Farooq Abstract Worldwide rice productivity is being threatened by increased endeavours of drought stress. Among the visible symptoms of drought stress, hampered water relations and disrupted cellular membrane functions are the most important. Exogenous use of polyamines (PAs), salicylic acid (SA), brassinosteroids (BRs), glycinebetaine (GB) and nitrous oxide (NO) can induce abiotic stresses tolerance in many crops. In this time course study, we appraised the comparative role of all these substances to improve the drought tolerance in rice (Oryza sativa L.) cultivar Super-Basmati. Plants were subjected to drought stress at four leaf stage (4 weeks after emergence) by maintaining soil moisture at 50 % of field capacity. Pre-optimized concentrations of GB (150 mg l,1), SA (100 mg l,1), NO (100 ,mol l,1 sodium nitroprusside as NO donor), BR (0.01 ,m 24-epibrassinolide) and spermine (Spm; 10 ,m) were foliar sprayed at five-leaf stage (5 weeks after emergence). There were two controls both receiving no foliar spray, viz. well watered (CK1) and drought stressed (CK2). There was substantial reduction in allometric response of rice, gas exchange and water relation attributes by drought stress. While drought stress enhanced the H2O2, malondialdehyde (MDA) and relative membrane permeability, foliar spray of all the chemicals improved growth possibly because of the improved carbon assimilation, enhanced synthesis of metabolites and maintenance of tissue water status. Simultaneous reduction in H2O2 and MDA production was also noted in the plants treated with these substances. Drought tolerance was sturdily associated with the greater tissue water potential, increased synthesis of metabolites and enhanced capacity of antioxidant system. Of all the chemicals, foliar spray with Spm was the most effective followed by BR. [source] Exogenously Applied Nitric Oxide Enhances the Drought Tolerance in Fine Grain Aromatic Rice (Oryza sativa L.)JOURNAL OF AGRONOMY AND CROP SCIENCE, Issue 4 2009M. Farooq Abstract Drought stress is a severe threat to the sustainable rice production, which causes oxidative damage and disturbs plant water relations, while exogenously applied nitric oxide (NO) may have the potential to alleviate these effects in rice plants. In this study, the role of NO to improve drought tolerance in fine grain aromatic rice (Oryza sativa L. cv. Basmati 2000) was evaluated. Sodium nitroprusside, a NO donor, was used at 50, 100 and 150 ,mol l,1 both as seed priming and foliar spray. To prime, the seeds were soaked in aerated NO solution of respective solution for 48 h and dried back to original weight. Primed and non-primed seeds were sown in plastic pots with normal irrigation in a greenhouse. At four leaf stage, plants were subjected to drought stress except the controls, which were kept at full field capacity. Drought was maintained at 50 % of field capacity by watering when needed. Two controls were maintained; both receiving no NO treatments as foliar application or seed treatment, one under drought conditions and the other under well-watered conditions. Drought stress seriously reduced the rice growth, but both methods of NO application alleviated the stress effects. Drought tolerance in rice was strongly related to the maintenance of tissue water potential and enhanced capacity of antioxidants, improved stability of cellular membranes and enhanced photosynthetic capacity, plausibly by signalling action of NO. Foliar treatments proved more effective than the seed treatments. Among NO treatment, 100 ,mol l,1 foliar spray was more effective. [source] Changes in synthesis and degradation of Rubisco and LHCII with leaf age in rice (Oryza sativa L.) growing under supplementary UV-B radiationPLANT CELL & ENVIRONMENT, Issue 6 2002A. Takeuchi Abstract The effects of supplementary ultraviolet-B (UV-B) radiation on the changes in synthesis and degradation of ribulose -1,5-bisphosphate carboxylase/oxygenase (Rubisco) and light-harvesting chlorophyll a/b binding protein of PSII (LHCII) were examined, as well as mRNA levels for small and large subunits of Rubisco (rbcS and rbcL, respectively) and LHCII (cab) with leaf age in UV-sensitive rice (Norin 1) and UV-resistant rice (Sasanishiki). Both Rubisco and LHCII were actively synthesized until the leaf had fully expanded, and then decreased with increasing leaf age. Synthesis of Rubisco, but not LHCII, was significantly suppressed by UV-B in Norin 1. The degradation of Rubisco was enhanced by UV-B around the time of leaf maturation in the two cultivars. The levels of rbcS and rbcL were reduced by UV-B at the early stages after leaf emergence in both cultivars. Cab transcripts were first present at high levels in the two cultivars, but drastically decreased due to UV-B treatment immediately after leaf emergence in Norin 1. It was shown that synthesis and degradation of Rubisco and LHCII greatly changed with leaf age: Rubisco synthesis was significantly suppressed by supplementary UV-B radiation at the transcription step during the early leaf stages. It was also suggested that the difference in UV-B sensitivity in Rubisco synthesis between the two rice cultivars might be due to specific suppression both transcriptionally and post-transcriptionally. [source] | |||||||||||||