Two Hymenophyllaceae species from contrasting natural environments exhibit a homoiochlorophyllous strategy in response to desiccation stress.

Hymenophyllaceae is a desiccation tolerant family of Pteridophytes which are poikilohydric epiphytes. Their fronds are composed by a single layer of cells and lack true mesophyll cells and stomata. Although they are associated with humid and shady environments, their vertical distribution varies along the trunk of the host plant with some species inhabiting the drier sides with a higher irradiance. The aim of this work was to compare the structure and function of the photosynthetic apparatus during desiccation and rehydration in two species, Hymenophyllum dentatum and Hymenoglossum cruentum, isolated from a contrasting vertical distribution along the trunk of their hosts. Both species were subjected to desiccation and rehydration kinetics to analyze frond phenotypic plasticity, as well as the structure, composition and function of the photosynthetic apparatus. Minimal differences in photosynthetic pigments were observed upon dehydration. Measurements of ϕPSII (effective quantum yield of PSII), ϕNPQ (quantum yield of the regulated energy dissipation of PSII), ϕNO (quantum yield of non-regulated energy dissipation of PSII), and TL (thermoluminescence) indicate that both species convert a functional photochemical apparatus into a structure which exhibits maximum quenching capacity in the dehydrated state with minimal changes in photosynthetic pigments and polypeptide compositions. This dehydration-induced conversion in the photosynthetic apparatus is completely reversible upon rehydration. We conclude that H. dentatum and H. cruentum are homoiochlorophyllous with respect to desiccation stress and exhibited no correlation between inherent desiccation tolerance and the vertical distribution along the host tree trunk.

Arsenic accumulation and distribution in relation to young seedling growth in Atriplex atacamensis Phil.

Even at trace levels, arsenic is of environmental and health concern due to its high toxicity. The xerohalophyte plant species Atriplex atacamensis grows on an arsenic-contaminated mining area in North Chile. Young seedlings that were grown from seeds collected from these plants were grown in a nutrient solution under controlled environmental conditions and were exposed for 14 and 28 days to 0, 100 or 1000 µM arsenate. More than 75% of the plants that were exposed to the highest As dose survived until the end of the treatment. The seedling growth was reduced (100 µM As) or inhibited (1000 µM As) in the stress conditions, but the plants were able to efficiently close their stomata and perform osmotic adjustments to avoid secondary water stress. Arsenic accumulated up to 400 µg g(-1) DW in the shoots and 3500 µg g(-1) DW in the roots. Arsenate drastically impaired the P content and increased glycinebetaine content, although no arsenobetaine was found in the tissues. With the exception of arsenite and arsenate, no As-containing organic compound was detected. Arsenic was not excreted by the trichomes that were present at the leaf surface. Although an increase in the total level of non-protein thiols suggested that arsenite fixation on the sulfhydryl groups could occur in the stressed tissues, the majority of the soluble arsenic remained in its oxidized state As(V). Arsenate induced an increase in the free soluble polyamine concentrations in all of the organs, and it increased the proportion of spermidine and spermine and decreased the proportion of putrescine in the polyamine pool. Therefore, it is likely that these polycationic molecules may assist in arsenate sequestration in the stressed tissues, and A. atacamensis may represent a promising plant species that can be tested in field trials for its phytomanagement of As-contaminated sites in desert areas.