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Abstract
Nitrogen (N) and silicon (Si) are two important nutritional elements required for plant growth, and both impact host plant resistance toward insect herbivores. The interaction between the two elements may therefore play a significant role in determining host plant resistance. We investigated this interaction in rice (Oryza sativa L.) and its effect on resistance to the herbivore brown planthopper Nilaparvata lugens (BPH). Our results indicate that high-level (5.76 mM) N fertilization reduced Si accumulation in rice leaves, and furthermore, this decrease was likely due to decreased expression of Si transporters OsLsi1 and OsLsi2. Conversely, reduced N accumulation was observed at high N fertilization levels when Si was exogenously provided, and this was associated with down-regulation of OsAMT1;1 and OsGS1;1, which are involved in ammonium uptake and assimilation, respectively. Under lower N fertilization levels (0.72 and/or 1.44 mM), Si amendment resulted in increased OsNRT1:1, OsGS2, OsFd-GOGAT, OsNADH-GOGAT2, and OsGDH2 expression. Additionally, bioassays revealed that high N fertilization level significantly decreased rice resistance to BPH, and the opposite effect was observed when Si was provided. These results provide additional insight into the antagonistic interaction between Si and N accumulation in rice, and the effects on plant growth and susceptibility to herbivores.
Highlights
Many studies have shown that plant anti-herbivore resistance is directly linked to physiological status, any factors affecting a plant’s physiology could potentially alter its resistance to insect pests (Slansky, 1990; Altieri and Nicholls, 2003)
At lower (0.72 and 1.44 mM) N fertilization levels, Si treatment tended to correlate with elevated OsNRT1;1, OsGS2, OsFdGOGAT, OsNADH-GOGAT2 and OsGDH2 transcript levels (Figures 5B,D–G), potentially identifying a feedback response mechanism operating under reduced N availability, which could at least partially account for the observed increases in plant dry weight and decreases in root/shoot ratios under reduced N conditions (Figures 1A,B; see Ericsson, 1995)
Our results show that an interaction exists between N and Si in rice
Summary
Many studies have shown that plant anti-herbivore resistance is directly linked to physiological status, any factors affecting a plant’s physiology could potentially alter its resistance to insect pests (Slansky, 1990; Altieri and Nicholls, 2003). The macronutrient nitrogen (N) is an essential element for growth and reproduction of both plants and animals, and has been considered critical for determining interactions between plants and their consumers, including herbivorous insects (Chen et al, 2008). Numerous studies have shown that high-level N fertilizer application to crops can influence plant-insect interactions, and potentially increase growth, food consumption, survival, reproductive rates and population densities of insect herbivores (Mattson, 1980; Moon et al, 1995; Brodbeck et al, 2001; Khan and Port, 2008). It has been demonstrated that the increasing populations of major insect pests of rice, including planthoppers, leaffolders, and stem borers, are closely related to the long-term excessive application of N fertilizers in most of the rice growing areas in Asia (Lu et al, 2007)
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