Effects of water deficit and its interaction with CO(2) supply on the biochemistry and physiology of photosynthesis in sunflower.
Photosynthetic responses of sunflower plants grown for 52 d in ambient and elevated CO(2) (A=350 or E=700 micromol mol(-1), respectively) and subjected to no (control), mild or severe water deficits after 45 d were analysed to determine if E modifies responses to water deficiency. Relative water content, leaf water potential (Psi(w)) and osmotic potential decreased with water deficiency, but there were no effects of E. Growth in E decreased stomatal conductance (g(s)) and thereby transpiration, but increased net CO(2) assimilation rate (P(n), short-term measurements); therefore, water-use efficiency increased by 230% (control plants) and 380% (severe stress). Growth in E did not affect the response of P(n) to intercellular CO(2) concentration, despite a reduction of 25% in Rubisco content, because this was compensated by a 32% increase in Rubisco activity. Analysis of chlorophyll a fluorescence showed that changes in energy metabolism associated with E were small, despite the decreased Rubisco content. Water deficits decreased g(s) and P(n): metabolic limitation was greater than stomatal at mild and severe deficit and was not overcome by elevated CO(2). The decrease in P(n) with water deficiency was related to lower Rubisco activity rather than to ATP and RuBP contents. Thus, there were no important interactions between CO(2) during growth and water deficit with respect to photosynthetic metabolism. Elevated CO(2 )will benefit sunflower growing under water deficit by marginally increasing P(n), and by slowing transpiration, which will decrease the rate and severity of water deficits, with limited effects on metabolism.
Tezara
W
W
Instituto de Biología Experimental, Universidad Central de Venezuela, Apartado 47114, Caracas 1041 A, Venezuela. wtezara@strix.ciens.ucv.ve
Mitchell
V
V
Driscoll
S P
SP
Lawlor
D W
DW
D000255:Adenosine Triphosphate / Q000378:metabolism; D001692:Biological Transport / Q000187:drug effects; D002245:Carbon Dioxide / Q000378:metabolism / Q000494:pharmacology*; D002734:Chlorophyll / Q000378:metabolism; D000077194:Chlorophyll A; D006368:Helianthus / Q000187:drug effects / Q000254:growth & development / Q000378:metabolism*; D045342:Light-Harvesting Protein Complexes; D009997:Osmotic Pressure / Q000187:drug effects; D010788:Photosynthesis / Q000187:drug effects / Q000502:physiology*; D045322:Photosynthetic Reaction Center Complex Proteins / Q000187:drug effects / Q000378:metabolism; D018515:Plant Leaves / Q000187:drug effects / Q000254:growth & development / Q000378:metabolism; D010940:Plant Proteins / Q000187:drug effects / Q000378:metabolism; D018526:Plant Transpiration / Q000187:drug effects; D012273:Ribulose-Bisphosphate Carboxylase / Q000187:drug effects / Q000378:metabolism; D012274:Ribulosephosphates / Q000378:metabolism; D013997:Time Factors; D014867:Water / Q000494:pharmacology / Q000502:physiology*
D045342:Light-Harvesting Protein Complexes; D045322:Photosynthetic Reaction Center Complex Proteins; D010940:Plant Proteins; D012274:Ribulosephosphates; D014867:Water; D002734:Chlorophyll; D002245:Carbon Dioxide; C001933:ribulose-1,5 diphosphate; D000255:Adenosine Triphosphate; D012273:Ribulose-Bisphosphate Carboxylase; D000077194:Chlorophyll A