Plant Science 180 (2011) 368–374 Contents lists available at ScienceDirect Plant Science journal homepage: www.elsevier.com/locate/plantsci Potassium deficiency affects water status and photosynthetic rate of the vegetative sink in green house tomato prior to its effects on source activity Synsuke Kanai a , Reda E. Moghaieb b , Hany A. El-Shemy c,∗ , R. Panigrahi d , Pravat K. Mohapatra f , J. Ito d , Nguyen T. Nguyen a , Hirofumi Saneoka a , Kounosuke Fujita e a Graduate School of Biosphere Science, Hiroshima University, 1-4-4 Kagamiyama, Higashi-hiroshima 739-8528, Japan b Genetic Department, Faculty of Agriculture, Cairo University, 12613 Giza, Egypt c Faculty of Agriculture Research Park (FARP) and Biochemistry Department, Faculty of Agriculture, Cairo University, 12613 Giza, Egypt d Hiroshima Prefectural Technology Research Institute, Hara, Hachihonmatsu, Higashi-hiroshima 739-8528, Japan e Professor Emeritus, Hiroshima University, 7-7-37 Nanaehama, Hokuto 049-0111, Japan f School of Life Science, Sambalpur University, Jyoti vihar, Sambalpur 768019, India article info Article history: Received 31 August 2010 Received in revised form 12 October 2010 Accepted 19 October 2010 Available online 26 October 2010 Keywords: Aquaporin K-channel Micro-morphometric method Potassium deficiency Stem diameter Tomato abstract The potassium requirement of green house tomatoes is very high for vegetative growth and fruit produc- tion. Potassium deficiency in plants takes long time for expression of visible symptoms. The objective of this study is to detect the deficiency early during the vegetative growth and define the roles of aquaporin and K-channel transporters in the process of regulation of water status and source–sink relationship. The tomato plants were grown hydroponically inside green house of Hiroshima University, Japan and subjected to different levels of K in the rooting medium. Potassium deficiency stress decreased photo- synthesis, expansion and transport of 14 C assimilates of the source leaf, but the effects became evident only after diameter expansion of the growing stem (sink) was down-regulated. The depression of stem diameter expansion is assumed to be associated with the suppression of water supply more than pho- tosynthate supply to the organ. The stem diameter expansion is parameterized by root water uptake and leaf transpiration rates. The application of aquaporin inhibitor (AgNO 3 ) decreased leaf water poten- tial, stem expansion and root hydraulic conductance within minutes of application. Similar results were obtained for application of the K-channel inhibitors. These observations suggested a close relationship between stem diameter expansion and activities of aquaporins and K-channel transporters in roots. The deficiency of potassium might have reduced aquaporin activity, consequently suppressing root hydraulic conductance and water supply to the growing stem for diameter expansion and leaf for transpiration. We conclude that close coupling between aquaporins and K-channel transporters in water uptake of roots is responsible for regulation of stem diameter dynamics of green house tomato plants. © 2010 Elsevier Ireland Ltd. All rights reserved. 1. Introduction Potassium requirement of green house tomato is very high for growth and fruit production [1]. The element is essential for pho- tosynthesis, enzyme activation, protein synthesis, cell turgor and ion homeostasis in plant cells [2]. K-deficiency, therefore, can dis- turb these activities directly, and restrict assimilate partitioning to the fruits from the source. However, deficiency symptoms of K do not immediately result in visible symptoms. The growth of the plant first decreases and then stops [3]; the visual deficiency of leaf ∗ Corresponding author at: Faculty of Agriculture Research Park (FARP) and Bio- chemistry Department, Faculty of Agriculture, Cairo University, 12613 Giza, Egypt. Tel.: +20 02 37742600; fax: +20 02 35717355. E-mail address: helshemy@hotmail.com (H.A. El-Shemy). necrosis appears after prolonged exposure to the stress [4]. Early detection of deficiency can retrieve the situation for the benefit of the farmers. But analytical techniques used for the purpose are lab- oratory intensive, cumbersome and time consuming. As of today, knowledge on the incidence of elastic strain (temporary), and the lag period necessary for switch over to plastic strain (permanent) [5] in response to the K-deficiency stress is scant. In our previ- ous work [6], a non-destructive technique (micro-morphometric technique) was used for monitoring K-deficiency during the early fruiting period of tomato. In this work, the instrument precisely recorded the fluctuation of diameters of potential sinks like stem and fruit of the plant, and correlated the changes to the water status of the organs. It was concluded that K-deficiency affected water status of the plant and reduced sink activity for assimilate consumption prior to its adverse effect on source activity (leaf photosynthesis). A similar approach was undertaken to monitor 0168-9452/$ – see front matter © 2010 Elsevier Ireland Ltd. All rights reserved. doi:10.1016/j.plantsci.2010.10.011