Abstract
We investigated the effects of P(SARK)IPT (for Senescence-Associated Receptor KinaseIsopentenyltransferase) expression and cytokinin production on several aspects of photosynthesis in transgenic tobacco (Nicotiana tabacum cv SR1) plants grown under optimal or restricted (30% of optimal) watering regimes. There were no significant differences in stomatal conductance between leaves from wild-type and transgenic P(SARK)-IPT plants grown under optimal or restricted watering. On the other hand, there was a significant reduction in the maximum rate of electron transport as well as the use of triose-phosphates only in wild-type plants during growth under restricted watering, indicating a biochemical control of photosynthesis during growth under water deficit. During water deficit conditions, the transgenic plants displayed an increase in catalase inside peroxisomes, maintained a physical association among chloroplasts, peroxisomes, and mitochondria, and increased the CO(2) compensation point, indicating the cytokinin-mediated occurrence of photorespiration in the transgenic plants. The contribution of photorespiration to the tolerance of transgenic plants to water deficit was also supported by the increase in transcripts coding for enzymes involved in the conversion of glycolate to ribulose-1,5-bisphosphate. Moreover, the increase in transcripts indicated a cytokinin-induced elevation in photorespiration, suggesting the contribution of photorespiration in the protection of photosynthetic processes and its beneficial role during water stress.
Highlights
We investigated the effects of PSARK::IPT expression and cytokinin production on several aspects of photosynthesis in transgenic tobacco (Nicotiana tabacum cv SR1) plants grown under optimal or restricted (30% of optimal) watering regimes
Our results show that during water stress, the production of CKs resulted in the protection of biochemical processes associated with photosynthesis and in the induction of photorespiration during water stress, which may contribute to the protection of photosynthesis during water stress
More pronounced was the decrease in A in wild-type plants after 20 d of growth under restricted watering. These results together with the biomass reduction observed in wild-type plants growing under restricted watering (Rivero et al, 2007) indicated that nonstomatal limitations to photosynthesis were the main factors inhibiting photosynthesis
Summary
We investigated the effects of PSARK::IPT (for Senescence-Associated Receptor Kinase::Isopentenyltransferase) expression and cytokinin production on several aspects of photosynthesis in transgenic tobacco (Nicotiana tabacum cv SR1) plants grown under optimal or restricted (30% of optimal) watering regimes. In an effort to overcome adverse physiological effects resulting from the manipulation of CKs, we developed transgenic plants that expressed IPT under the control of Senescence-Associated Receptor Kinase (SARK; Hajouj et al, 2000), a maturation- and stress-inducible promoter (Rivero et al, 2007). We investigated further the effects of PSARK::IPT expression and CK production on several aspects of photosynthesis in transgenic tobacco plants grown under optimal or restricted watering regimes. Our results show that during water stress, the production of CKs resulted in the protection of biochemical processes associated with photosynthesis and in the induction of photorespiration during water stress, which may contribute to the protection of photosynthesis during water stress
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