不同磷营养水平对烟草叶片光合作用和光呼吸的影响

Effects of Inorganic Phosphate Nutrition on Photosynthesis and Photorespiration in Tobacco Leaves

随着磷营养水平的提高,烟草叶片的CO_2补偿点下降、光合速率上升。光呼吸在缺磷时最高。用光呼吸抑制剂处理烟草叶片后,光合的最适磷浓度提高。当CO_2浓度为560μl/L时,缺磷的烟草叶片在从21％O_2转入2％O_2时出现光合振荡,表明光呼吸与磷营养有密切关系。光呼吸在形成乙醇酸时所释放的磷,有回补叶绿体进行光合作用所需的磷的作用。

Photosynthetic and photorespira-tion rates and CO_2 compensation pointof leaves of tobacco plants grown atvarious phosphate levels (0, 1/8, 1/4,1/2, 1 P, 1 P is the normal phosphatecontent in Hoagland's solution) weredetermined by infra-red CO_2 analyzer.CO_2 compensation point decreased withincreasing phosphate level, being 125ppm in leaves treated with 0 P and 75ppm with 1 P nutrition(Fig. 1). Pho-tosynthetic rate increased graduallywith increasing phosphate levels underthree CO_2 concentrations (130, 190and 350 ul/L). The Same tendency ofchanges of photorespiration rate wasfound when the phosphate nutritionchanged from 1/4 P to 1 P. The maxi-mum value of photorespiration rate,however, was found in leaves with 0 Pnutrition. The ratio of photorespira-tion/photosynthesis decreased with in-creasing phosphate nutrition. The re-sults (Fig. 2) suggested that phosphatedeficiency stimulated the rate of pho-torespiration but diminished that ofphotosynthesis. Vacuum infiltration ofleaf discs of tobacco grown under nor-mal phospate nutrition with an in-hibitor of glycolate oxidase, α-HPMS(0. 4 mmol/L), or with an inhibitorof glycolate synthesis, glycidate (20mmol/L), showed that the optimumphosphate concentration for photosyn-thesis was increased, α-HPMS beingmore effective than glycidate (Fig. 3,4). This implies that inhibition of pho-torespiration results in an increase ofphosphate requirement for photosyn-thesis. At CO_2 concentration of 560 ul/Land after transition from 21 % to 2%O_2, oscillation of photosynthesis wasobserved in tobacco leaves with 0 Pand 1/8 P nutrition (Fig. 5). According to the above results weconcluded that photorespiration wasstimulated by phosphate deficiency,and the increase in photorespirationcould compensate for the phosphateused in photosynthesis, through theproduction of phosphoglycolate byRuBP oxygenase followed by its hy-drolysis by phosphatase within thechloroplasts.