Proceedings of the XLVI Italian Society of Agricultural Genetics - SIGA Annual Congress

Giardini Naxos, Italy - 18/21 September, 2002

ISBN 88-900622-3-1

Poster Abstract - 1.32

Recovering of photosynthetic rate efficiency in Arbutus unedo after INDUCED DROUGHT and salt stress

PICCINELLI D.*, LORETO F.**, LAI A.*

*) Enea C.R. Frascati FIS – LAS, Via Enrico Fermi 45, 00044 Frascati, Roma

**) CNR Monterotondo Scalo IBEV, Via Salaria Km 29,300, 00016 Monterotondo Scalo, Roma

Arbutus unedo, photosynthetic rate, drought stress, salt stress

The sclerophyll evergreen plants prevail in the Mediterranean area. Their leaves present xeromorphic features which are suitable to the life in a dry environment. Arbutus unedo, among the plants peculiar of the Mediterranean shrub, seems extremely interesting, because its photosynthetic level, the physiological behaviour and stomatal patchiness make it comparable to the tree-type plants more extensively used in food and agriculture.

The purpose of the present investigation, performed at the ENEA C.R. Frascati, with the contribution of CNR at Montelibretti (Roma), was the follow-up of the re-establishment of photosynthesis after a period of drought or salt stress in Arbutus unedo plants.

The conditions of an inshore area were re-created, by artificially and separately inducing a water stress (un-watered plants) and a salt stress (plants watered by a 1% NaCl solution). After 30 days, the plants were regularly watered and the photosynthetic parameters (CO2 and H2O exchange and chlorophyll fluorescence) were evaluated at 6, 13, 21 and 25 days intervals. At the same time the RWC (Relative Water Content) and the sodium content of the leaves were measured.Both the plants under salt stress (Na plants) and those under drought (D plants) undergo a photoinhibition process, but this showed recovery evidence already 6 days after the stress relief.

When the stress was most acute, D plants showed a photosynthetic rate about 97 % lower than the control plants, whereas this reduction was only 50% in Na plants.

After 25 days of recovery both D and Na plants showed a photosynthesis rate not statistically different from the control plants. However, before this date the recovery of the photosynthetic activity was fast and continuous in D plants, but slow and irregular in Na plants.

Chlorophyll fluorescence measurements indicated no damage to the PSII quantum yield both in D and Na plants.

Inhibition and recovery of the stomatal and biochemistry functions were also dependent on the stress imposed but were linearly connected to the photosynthesis process. While stomatal closure occurred gradually with the stress onset, the inhibition of the Rubisco (Ribulose I,5-bisphosphate carboxilase-oxigenase) activity occurred solely during the highest stress step and was more evident within the D plants than within the Na plants; nevertheless after 25 days of recovery the Rubisco activity reaches that of control plants irrespective of the stress imposed.

The salt built up during the Na treatment and was only partially removed after 25 days of recovery, but the salt quantity inside the leaves does not seem to be directly linked to the rate of photoinhibition, even if the photosynthesis levels are not consistent with the ones in the control plants.

Sodium content differences were significant in the leaves of different plants . By comparing the photosynthesis activity of these plants, different response mechanism to the stress of genetic origin can be suggested. Further investigation on that matter will be carried out.