The Effect of Salinity upon Photosynthesis in Rice (Oryza sativa L.): Gas Exchange by Individual Leaves in relation to their Salt Content

Yeo, A. R., Caporn, S. J. M.and Flowers, T. J. 1985. The effectof salinity upon photosynthesis in rice (Oryza sativa L.): Gasexchange by individual leaves in relation to their salt content.—J.exp. Bot. 36: 1240–1248. The effect of salinity upon net photosynthesis and transpirationby individual leaves of rice has been investigated by gas exchangemeasurements in seedlings at the five to six leaf stage. Salinitydid not, initially, reduce net photosynthesis in the whole plantbut only in the older leaves in which sodium accumulated. Analysisof the course of events in leaf four following salinizationof the medium showed that net photosynthesis was inversely correlatedwith the sodium concentration in the leaf tissue. There wasno evidence of a threshold effect; net photosynthesis declinedlinearly with increasing leaf sodium concentration and was reducedby 50% at only 05 mmol sodium per gram dry weight. The relationshipbetween transpiration rate and leaf sodium concentration closelyparalleled that for photosynthesis; there was no effect of leafsodium concentration on the carbon dioxide concentration inthe intercellular spaces, showing that sodium accumulation inthe leaf affected stomatal aperture and carbon dioxide fixationsimultaneously. Photosynthesis was reduced by half at a sodiumconcentration in the leaf which did not reduce the concentrationof chlorophyll. The nature of the effect of salinity upon leafgas exchange is discussed. Key words: Salinity, rice, Oryza sativa L., photosynthesis, apoplastic salt load     

Effects of Atmospheric Humidity on Abscisic Acid Accumulation and Water Status in Leaves of Rice (Oryza sativa L.)

Rice (Oryza sativa L ) plants were grown in controlled environmentcabinets with either low (c 0 4 kPa) or high (c 1 6 kPa) atmosphericwater vapour pressure deficit (v p d) The capacity of detachedleaves to accumulate ABA in response to rapidly induced waterstress was increased when plants were grown at high v p d Highv p d significantly lowered solute potential (     

Abscisic Acid Accumulation in Detached Leaves of Rice (Oryza sativa L.) in Response to Water Stress: A Correlation with Leaf Size

When water stress was imposed on detached leaves of two rice(Oryza sativa L.) cultivars, more ABA per unit fresh weightaccumulated in IR20, a small-leaved cultivar, than in 63–83,a large-leaved cultivar; the difference being up to threefold.In an F₂ population of a cross between the two cultivars ABAaccumulation was found to be significantly negatively correlatedwith leaf fresh weight. This correlation persisted in the F₃generation. Such a correlation was not evident, however, whena number of rice cultivars, which varied widely in leaf size,were examined. The difference in ABA accumulation between IR20 and 63–83was not accounted for by different spatial patterns of waterloss or ABA accumulation within a leaf, and cultivar differencesin ABA content were maintained both across, and at various positionsalong the leaf. No major differences in leaf anatomy were observed between thetwo cultivars. Differences found in leaf water relations characteristicswere few and generally minor. It therefore seems unlikely thatthese properties account for the difference between the cultivarsin the ability to accumulate ABA or for the correlation withleaf size. Oryza sativa L, rice, water stress, abscisic acid, leaf size     

Abscisic Acid and Water Relations of Rice (Oryza sativa L.): Effects of Drought Conditioning on Abscisic Acid Accumulation in the Leaf and Stomatal Response

The effects of a period of water stress (drought conditioning)on responses to a second (challenge) stress were examined inyoung vegetative rice (Oryza sativa L.) plants. Drought conditioningdid not affect the rate of subsequent stress development, nor,in a first experiment, did it influence relations between turgor(_p) and total () leaf water potential. However, conditioningdid extend the range of _p over which stomata remained open andsignificantly reduced the amount of ABA which accumulated inthe leaf at a given _p. The change in stomatal behaviour (stomataladjustment) was quantitatively accounted for by the change inleaf ABA accumulation. The reduction in ABA accumulation due to conditioning did notinvolve a change in the potential capacity to produce ABA, asABA accumulation in partially dehydrated detached leaves wasnot reduced by conditioning. It is suggested that effects ofconditioning on leaf ABA content in the intact plant involvechanges in the rate of ABA export from the leaf. Oryza sativa L, rice, drought conditioning, stomata, water stress, abscisic acid