| Photosynthesis in wheat as influenced by leaf position,
time of the day and presence of the sink M.C. GHILDIYAL, D.C. UPRETY and G.S. SIROHI Division of Plant Physiology Indian Agricultural Research Institute New Delhi-110012, India Photosynthesis is the major component of biomass production. Photosynthetic potential depends on the area of the leaves and their photosynthetic efficiency over the growing period. Generally the uppermost fully expanded leaves were examined and measurements were made once in a day to characterise the photosynthesis rate of the plant (GIFFORD & EVANS 1981). There are reports however, of variation in photosynthesis rate among different leaves (DANTUMA 1973: HODANOVA 1981). Diurnal changes in photosynthesis rate have been reported in other species (UPMEYER & KOLLER 1973, PALLAS et al. 1974, KERR et al. 1985). One of the important factors which influences the rate of photosynthesis is the sink capacity (NEALES & INCOLL 1968, GIFFORD & EVANS 1981). In wheat, removal of sink (ear) led to inhibition of flag leaf photosynthesis (KlNG et al. 1967). AUSTIN & EDRICH (1975) however, were unable to confirm the ear removal response. In the present investigation we have examined some of these aspects in an T. aestivum wheat cultivar Kalyansona. Materials and Methods Wheat (Triticum aestivum) cultivar Kalyansona was raised in earthen pots (35 x 40 cm) containing sandy loam soil. Fertilizers were supplied at the rate of 120, 60 and 60 ppm respectively of N, P and K. N was supplied in two split doses, whereas P and K were given only at the time of sowing. Four healthy plants were kept in each pot which formed one replication. There were six replications for every determination at each sampling occasion. Photosynthesis rate was measured by a battery portable infrared CO2 analyser (ADC; UK) under saturated light conditions (PARKINSON et al. 1980). Parkinson leaf chamber for cereal leaves was used. Rate of photosynthesis was examined in the uppermost fully expanded leaf of main shoot (MS) 23 and 18 days before anthesis, at anthesis and 10 and 20 days after anthesis to examine changes in the rate during ontogeny. The rate of photosynthesis of the leaves at different position in the main shoot was examined at pre-anthesis, anthesis and post anthesis stages. Photosynthesis rate and stomatal diffusive resistance of the uppermost fully expanded leaf/flag leaf of the main shoot was also examined hourly from 10 AM to 4 PM at pre-anthesis, anthesis and post anthesis stages. The stomatal diffusive resistance was measured by a steady state porometer (Li- Cor LI 1600). In order to examine the effect of sink on photosynthesis rate, ear removal treatments were given. In one of the treatments MS ears were removed as soon as they emerged whereas, in another, ears of both MS and tillers were removed. Photosynthesis rate of the flag leaf of main shoot of control and de-eared plants was examined 10 and 20 days after anthesis observed in MS of control plants. The dry matter yields were recorded at the time of harvest. |
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