ORIGINAL ARTICLE High day–night transition temperature alters nocturnal starch metabolism in rice (Oryza sativa L.) Nitin Sharma 1 • Archana Yadav 1 • Sangeeta Khetarpal 1 • Anjali Anand 1 • Lekshmy Sathee 1 • Ranjeet Ranjan Kumar 2 • Bhupinder Singh 3 • Naresh Kumar Soora 3 • Suchitra Pushkar 1 Received: 5 December 2016 / Revised: 12 January 2017 / Accepted: 1 February 2017 Ó Franciszek Go ´rski Institute of Plant Physiology, Polish Academy of Sciences, Krako ´w 2017 Abstract Transitory starch plays a vital role in mainte- nance respiration as its degradation products provide sub- strate for the night respiration. A study was conducted with two contrasting rice cultivars: Vandana (high night tem- perature susceptible) and Nagina 22 (high night tempera- ture tolerant) by subjecting them to increase in transition temperature from anthesis to physiological maturity. Night respiration on plant area basis increased by 35% in Van- dana at 5 days after anthesis but was unaffected in tolerant cultivar. A simultaneous 18% decrease in starch content was observed in the susceptible cultivar. An analysis of the starch-metabolizing enzymes showed that activity of b- amylase increased markedly in Vandana whereas both b and a-amylase decreased in Nagina 22 following high day to night transition temperature exposure. The level of starch breakdown product, maltose, increased in the sus- ceptible cultivar but glucose levels declined in both the cultivars. Concurrently, expression of chloroplastic iso- forms a-amylase OsAMY1, OsAMY2 and b-amylase OsBAM2 increased in Vandana. A lower accumulation of dry matter was recorded in the susceptible than the tolerant cultivar. Our study elucidated the regulatory role of tran- sitory starch in supporting the high day to night transition temperature-induced night-time respiration which is mediated by the increased activity of b-amylase through enhanced expression of OsBAM2 in flag leaves of sus- ceptible cultivar. Keywords Amylase  High night temperature (HNT)  Maltose  Respiration  Rice  Starch Communicated by B Zheng. N. Sharma and A. Yadav contributed equally to this work. & Anjali Anand anjaliiari@gmail.com Nitin Sharma ntnsharma27@gmail.com Archana Yadav yadavarchana1904@gmail.com Sangeeta Khetarpal sk16mk@gmail.com Lekshmy Sathee lekshmyrnair@gmail.com Ranjeet Ranjan Kumar ranjeetranjaniari@gmail.com Bhupinder Singh bhupindersinghiari@yahoo.com Naresh Kumar Soora nareshkumar.soora@gmail.com Suchitra Pushkar suchi.iari@gmail.com 1 Division of Plant Physiology, Indian Agricultural Research Institute, New Delhi 110 012, India 2 Division of Biochemistry, Indian Agricultural Research Institute, New Delhi 110 012, India 3 Centre for Environment Science and Climate Resilient Agriculture, Indian Agricultural Research Institute, New Delhi 110 012, India 123 Acta Physiol Plant (2017) 39:74 DOI 10.1007/s11738-017-2370-4