Chlorophyll fluorescencein vivo as an indicator of water stress in potato leaves

Potato plants, cv. Desirée, were exposed to a -0.3 MPa polyethylene glycol-induced water stress for 24 h in a hydroponic system. Leaves with a Leaf Plastochron Index of 3 to 3.99, 4 to 4.99 and 6 to 6.99 were measured for total, osmotic and pressure potential, leaf conductance andin vivo chlorophyll fluorescence transients F_o, F_p and F_T. Leaf conductance and F_o significantly declined with leaf age in unstressed leaves. Water potential components and leaf conductance were significantly lower after 4 h of water stress whereas all three chlorophyll fluorescence transients measured after 24 h were significantly higher. The increase in fluorescence transients suggested that PSII electron acceptors were reduced faster than PSI and the Calvin cycle could oxidize them.In vivo chlorophyll fluorescence provides a greater understanding of the physiological effects of water stress but it requires additional experimentation to make it useful in screening for water stress tolerance.