Functional Characterization of the Photosynthetic Machinery in Smicronix Galls on the Parasitic Plant Cuscuta campestris by JIP-Test

Members of the genus Cuscuta are generally considered to be non-photosynthetic, stem-holoparasitic flowering plants. Under certain circumstances, at least some members of the genus are capable of limited photosynthesis. The galls of the Smicronyx weevils formed on Cuscuta campestris are particularly rich in chlorophylls compared to the stem of the parasitic plant. In the present study, we aimed to characterize the photosynthetic activity in the inner and outer gall cortices in comparison to the non-photosynthetic stems and a reference plant (Arabidopsis thaliana). The recorded prompt chlorophyll fluorescence transients were analyzed using JIP test. Detailed analysis of the chlorophyll fluorescence confirmed the presence of actively functioning photosynthetic machinery, especially in the inner cortex of the galls. This photosynthesis, induced by the insect larvae, did not reach the levels of the photosynthetic activity in Arabidopsis thaliana plants. Thylakoid protein complexes were identified by separation with two-dimensional Blue Native/SDS PAGE. It appeared that some of the complexes presented in A. thaliana are missing in C. campestris. We hypothesize that the insect-triggered transition from non-photosynthetic to photosynthetic tissue in the gall is driven by the increased requirements for nutrients related to the larval nutrition.

Photochemical responses of cucumber (Cucumis sativus L.) plants to heat stress

In this study, photochemical responses of cucumber (Cucumis sativus L.) cultivar, ‘Beith Alpha F1’, under moderate and severe heat stress (45 °C and 55 °C, 4 hours) was studied. Chlorophyll a fluorescence measurement and the results of the JIP test indicated that severe heat stress was more drastically affected the photosynthetic activity as compared to moderate heat stress in the cotyledons of cucumber plants. Severe heat stress, for example, led to the increased level of Fo and decreased level of Fm, Fv/Fo, and Fv/Fm, suggesting remarkable photoinhibition on electron transport reactions in cucumber plants. Also, severe heat stress caused the increased level of accumulation of inactive reaction centers, resulting in a decreased amount of trapped light energy and electron transport on PSII. The enhanced values of DIo/RC and fDo in the cotyledons of cucumber plants indicated that the trapped energy cannot be used for photochemical reactions and lost as heat. Consequently, the reduction of the plastoquinone pool was partly inhibited due to the decreased yield of photochemistry. As a result, it may be concluded that severe heat stress inhibited PSII activity in several points and decreased photosynthetic yield in the cotyledons of cucumber plants.