K. SOWJANYA SREE, KLAUS-J. APPENROTH
Amity Institute of Microbial Technology, Amity University, Noida, Uttar Pradesh, India
Institute of Plant Physiology, University of Jena, Jena, Germany
*For correspondence: Klaus-J. Appenroth, University of Jena, Institute of Plant Physiology, Dornburger Str. 159, D-07743 Jena, Germany. Email: Klaus.Appenroth@uni-jena.de Phone: +49 3641 949233, Fax: +49 3641 949232
Abiotic stresses often result in suppression of photosynthesis and plant growth. Using the duckweed species Lemna minor and subjecting these plants to abiotic stress viz., (1) application of heavy metals, (2) application of salt (NaCl), and (3) lack of phosphate, we showed that photosynthesis was inhibited to a lesser degree than plant growth. This became evident by detecting the accumulation of starch under these conditions: (1) Cadmium ions and other heavy metals induced the accumulation of starch after 4 days of treatment at concentrations when growth was almost completely suppressed (e. g. 80 %). (2) Application of NaCl at a concentration of 150 mM also resulted in accumulation of starch but the highest level could be observed only after 7 days. (3) Depletion of phosphate in the growth medium had similar effects leading to starch accumulation after 14 days of treatment. Starch can accumulate to approximately 50% of dry mass under the three different conditions. We suggest the following common molecular mechanism: The stress factor suppresses growth more effectively than photosynthesis. The resulting surplus of carbohydrates is then stored as starch. This hypothesis has biotechnological relevance since stressors may be applied for increasing starch accumulation in duckweed and thus could be used to optimize bioethanol production from this aquatic crop.
Key words: Duckweed, Lemna minor, Lemnaceae, Starch accumulation, stress responses