A field portable method for the semi-quantitative estimation of dehydration tolerance of photosynthetic tissues across distantly related land plants.

Abstract

Desiccation tolerant (DT) plants withstand complete cellular dehydration (reaching relative water contents below 30% in their photosynthetic tissues), while desiccation sensitive (DS) plants exhibit different degrees of dehydration tolerance (DHT), never surviving water loss >70%. To date, no procedure for the quantitative evaluation of DHT extent exists that is able to discriminate DS species with different degrees of DHT from truly DT plants. We developed a simple, feasible, and portable protocol to differentiate between constitutive DT and different degrees of DHT in photosynthetic tissues. The protocol is based on (i) controlled desiccation inside Falcon tubes equilibrated at three different relative humidities (RH: 80%, 50% and <10%) and (ii) evaluation of the average recovery level of maximal photochemical efficiency (Fv/Fm) after rehydration. Applying the method to 10 bryophytes and 28 tracheophytes from various locations, we found that (i) imbibition of absorbent material with saturated salt solutions inside the tubes provides stable RH and avoids direct contact with samples; (ii) for 50 mL capacity tubes, the optimal initial plant amount is 50–200 mg FW; (iii) the tubes can be re-used up to three times with very little changes in RH; (iv) the method is useful in remote locations due to minimal instrumental requirements; (v) a threshold of 30% recovery of the initial Fv/Fm correctly categorises DT species with a few exceptions among tracheophytes: poikilochorophyllous DT-species and some DS herbs and gymnosperms. The protocol provides a semi-quantitative expression of DHT that facilitates comparisons of species with different morpho-physiological traits and/or ecological attributes.