Chin J Plan Ecolo ›› 2003, Vol. 27 ›› Issue (2): 196-201.

• Research Articles •

### Effect o Potassium on Sucrose Content of Flag Leaves and Starch Accumulation of Kernels in Wheat

WANG Xu-Dong, YU Zhen-Wen and WANG Dong

• Online:2003-02-10 Published:2012-09-26
• Contact: WANG Xu-Dong

Abstract:

There has been a phenomenon in wheat production of attaching importance to nitrogen fertilizer but ignoring potassium fertilizer. Employing nitrogen fertilizer solely results in excessively growing, soft stemmed, wheat, leading to a reduction in kernel yield. Also, the soil hardens and the environment is destroyed. As one of the indispensable elements, potassium has become an important limiting factor in wheat kernel yield increasing. This article studied the effect of potassium on photosynthetic rate, sucrose content, activity of sucrose_phosphate synthase (SPS)—the key enzyme in sucrose synthesis—in flag leaves, and on the sucrose content, activity of sucrose synthase (SS) (the key enzyme in sucrose decomposition), activity of adenosine phosphorate glucose pyrophrylase (ADPGPPase) (the key enzyme in starch formation), and starch accumulation rate of kernels of wheat. The study was carried out in 1999 on an experimental farm of Shandong Agricultural University, Taian,China,using the variety `Lumai 22’which has high yield potential. The experiment set three potassium treatments (K0, K1 and K2); the potassium amounts supplied were 0 kg K2O, 168.75kg K2O, 225.00 kg K2O per hm2 respectively,using KCl as the potassium fertilizer. Each treatment had three replicates. The plot area was 2 m×6 m=12 m2, with sowing on October 11 in 1999. The basic seedling number was 120 per m2. Single stems flowering on the same day were selected and marked using hanging cards during the anthesis period. These marked stems were used as the sample. The results suggest that potassium can prolong the peak period of photosynthetic rate, increase the supply of photosynthetic products in flag leaves, improve the activity of SPS after anthesis, accelerate sucrose synthesis during the early and middle periods of kernel filling in flag leaves, and increase sucrose content in flag leaves. Potassium also enhanced the supply of sucrose in the kernel during kernel filling, increased the activity of SS which favors sucrose decomposition in the kernel, and produces sufficient precursor for starch synthesis; improved the activity of ADPGPPase which favors starch formation; accelerated the rate of starch accumulation during the peak period of starch synthesis, and finally increased spike number, kernel weight and yield in wheat. Among the three treatments, each index had the greatest value in the K1 treatment. So the K1 treatment produced the highest kernel yield.The physiological effects of potassium on yield in wheat were discussed from two points of view, namely, from the point of photosynthetic product supplying intensity in flag leaves and precursor supplying intensity in kernel sink, concentrating on key enzymes. It was considered that potassium could increase kernel weight and yield by increasing the activity of SPS in the flag leaf and increasing the activities of SS and ADPGPPase in the kernel, but the physiological and biochemical mechanisms underlying this action should be investigated further. Furthermore, this article also discussed the reason why the K1 treatment is superior to the K2 treatment. It is possible that root absorption of K+ and NO-3 -N are inter- related, and so an excessive K+ concentration could affect the absorption of NO-3 -N in the root. This would result in an effect on nitrogen absorption and transportation throughout the wheat plant, causing a reduction in wheat yield. The physiological mechanisms behind this effect require further study.