Local induction of senescence by darkness in Cucurbita pepo (zucchini) cotyledons or the primary leaf induces opposite effects in the adjacent illuminated organ

Ananieva K., Ananiev E.D., Doncheva S., Stefanov D., Mishev K., Kamínek M., Motyka V., Dobrev P.I., Malbeck J.

Klíčová slova: Abscisic acid, cotyledons, cytokinins, cytokinin oxidase/dehydrogenase, dark treatment, primary leaves
Abstrakt: Local darkening of zucchini cotyledons or the primary leaf affected in an organ-specific manner the adjacent ones which remained under the initial light regime. Individual darkening of either the pair of cotyledons or the primary leaf led to acceleration of senescence expressed by lowering of chlorophyll content and net photosynthetic rate. Darkening of the pair of cotyledons induced a reduction in total cytokinin (CK) levels and increased CK oxidase/dehydrogenase (CKX) activity in the adjacent illuminated primary leaf. In addition, abscisic acid (ABA) content was increased which correlated with reduced stomatal aperture leading to decreased stomatal conductance and transpiration rate. In contrast, darkening of the adjacent primary leaf led to increased metabolic activity in the illuminated cotyledons including increased total CK levels in parallel with decreased CKX activity, decreased ABA content in correlation with increased stomatal aperture, stomatal conductance and transpiration rate. On the other hand, the functional activity of the photosynthetic apparatus as well as the transcript levels of the three photosynthesis-related genes psbA, psaB and rbcL remained almost unaffected in both illuminated organs. Thus, compared with the primary leaves, cotyledons appeared to be much more resistant to the dark stress applied either directly or to the adjacent primary leaf. Our results indicated the involvement of CKs and ABA signalling in the control of the communication mechanisms between cotyledons and the primary leaf that could operate in response to changing environmental factors like shading during earlier stages of plant development.
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Autoři z ÚEB: Petre I. Dobrev, Miroslav Kamínek, Jiří Malbeck, Václav Motyka