Potassium (K) deficiency is one of the major abiotic stresses which has drastically influenced maize growth and yield around the world. However, the physiological mechanism of K deficiency tolerance is not yet fully understood. To identify the differences of root morphology, physiology and endogenous hormones at different growing stages, two maize inbred lines 90-21-3 (tolerance to K deficiency) and D937 (sensitive to K deficiency) were cultivated in the long-term K fertilizer experimental pool under high potassium (+K) and low potassium (–K) treatments. The results indicated that the root length, volume and surface area of 90-21-3 were significantly higher than those of D937 under –K treatment at different growing stages. It was noteworthy that the lateral roots of 90-21-3 were dramatically higher than those of D937 at tasselling and flowering stage under –K treatment. Meanwhile, the values of superoxide dismutase (SOD) and oxidizing force of 90-21-3 were apparently higher than those of D937, whereas malondialdehyde (MDA) content of D937 was obviously increased. Compared with +K treatment, the indole-3-acetic acid (IAA) content of 90-21-3 was largely increased under –K treatment, whereas it was sharply decreased in D937. On the contrary, abscisic acid (ABA) content of 90-21-3 was slightly increased, but that of D937 was significantly increased. The zeatin riboside (ZR) content of 90-21-3 was significantly decreased, while that of D937 was relatively increased. These results indicated that the endogenous hormones were stimulated in 90-21-3 to adjust lateral root development and to maintain the physiology function thereby alleviating K deficiency.

Soybean root and stem rot caused by Phytophthora sojae is a destructive disease worldwide. Using genetic resistance is an important and major component in the integrated pest management of this disease. To understand molecular mechanisms of root and stem rot resistance in soybeans, the gene and protein expression in hypocotyls and stems of variety Suinong 10 carrying resistance genes Rps1a and Rps2 was investigated by using mRNA differential display reverse transcription PCR and two-dimensional electrophoresis at 0, 0.5, 1, 2, and 4 h after inoculation with P. sojae race 1. The results of the comparison of gene and protein expression showed that at least eight differential fragments at the transcriptional level were related to metabolic pathway, phytoalexin, and signal transduction in defense responses.Sequence analyses indicated that these fragments represented cinnamic acid 4-hydroxylase gene, ATP β gene coding ATP synthase β subunit and ubiquitin-conjugating enzyme gene which upregulated at 0.5 h post inoculation, blue copper protein gene and UDP-N-acetyl-α-D-galactosamine gene which upregulated at 2 h post inoculation, TGA-type basic leucine zipper protein TGA1.1 gene, cyclophilin gene, and 14-3-3 protein gene which upregulated at 4 h post inoculation.Three resistance-related proteins, α-subunit and β-subunit of ATP synthase, and cytochrome P450-like protein, were upregulated at 2 h post inoculation. The results suggested that resistance-related multiple proteins and genes were expressed in the recognition between soybean and P. sojae during zoospore germination, penetration and mycelium growth of P. sojae in soybean.