PHOTOSYNTHETICA

Photosynthetica 2006, 44(4):569-578 | DOI: 10.1007/s11099-006-0073-y

Photosynthetic response of different pea cultivars to low and high temperature treatments

K. Georgieva^1,2, H. K. Lichtenthaler^1,*

¹ Botanisches Institut II (Molekularbiologie und Biochemie der Pflanzen), Universität Karlsruhe, Karlsruhe, Germany

² Institute of Plant Physiology, Bulgarian Academy of Sciences, Sofia, Bulgaria

The thermo-sensitivity of two new pea (Pisum sativum L.) cultivars-Afila (mutant in the gene transforming leaves into mustaches) and Ranen (mutant for early ripening)-as compared to the control cultivar Pleven-4 to either low (4 °C, T₄) or high temperature (38 °C, T₃₈) was investigated by means of chlorophyll (Chl) fluorescence kinetics. The low temperature treatment decreased the photosynthetic activity, measured via a decline of the Chl fluorescence decrease ratios R_Fd690 and R_Fd735, and this was mainly due to a decline of the Chl fluorescence decrease parameter F_d and maximum Chl fluorescence F_m. In the new cv. Ranen the R_Fd ratios at first decreased and increased again after 24-h exposure to 4 °C, indicating its good acclimation ability to low temperature. The cold-induced changes in the photosynthetic performance of all cultivars were reversed after transferring plants back to 23 °C for 48 h. In the Chl and carotenoid (Car) contents no or little changes occurred during the T₄ treatment, except for a slight but clear increase of the ratio Chl a/b and a decrease in the ratio Chl/Car. In contrast to this, the T₃₈ treatment for 72 h decreased the R_Fd ratios more strongly than the T₄ exposure did. In fact, an irreversible injury of the photosynthetic apparatus was caused in the control pea cv. Pleven-4 by a 48-h T₃₈ exposure and for the new cv. Afila after a 72-h T₃₈ exposure. In contrast, the cv. Ranen was less and little sensitive to the T₃₈ exposure. In the heat-sensitive cvs. Pleven-4 and Afila, the decrease in R_Fd values at T₃₈ was associated with a strong decline of the Chl a+b and total Car contents. The Chl a+b decline could also be followed via an increase of the Chl fluorescence ratio F₆₉₀/F₇₃₅. Parallel to this, a strong decline of Chl a/b from ca. 3.0 (range 2.85-3.15) to ca. 1.9 (range 1.85-1.95) occurred indicating a preferential decline of the Chl a-pigment proteins but not of the Chl a/b-pigment protein LHC2. In the relatively heat-tolerant cv. Ranen, however, the ratio Chl a/b declined only partially. After the T₄ treatment the stress adaptation index Ap was higher in cv. Ranen than in controls and reached in heat-treated Ranen plants almost the starting value indicating a cold and heat stress hardening of the treated plants. The Chl fluorescence parameters and pigment contents were influenced by T₃₈ and T₄ treatments in various ways indicating that the mechanisms of low and high temperature injury of the photosynthetic apparatus are different. The new cv. Ranen exhibited a cross tolerance showing a fairly good acclimation ability to both T₄ and T₃₈, hence it is a very suitable plant for outdoor growth and for clarification of the acclimation mechanisms to unfavourable temperatures.

Additional key words: chlorophyll fluorescence; chlorophyll fluorescence decrease ratio; cultivar differences; Pisum; vR_Fd-values; stress adaptation index; thermo-sensitivity

Received: November 4, 2005; Accepted: April 24, 2006; Published: December 1, 2006  Show citation