Crop productivity is greatly influenced by various environmental stresses, of which insect herbivory-induced biotic stress assumes much significance. As a consequence of insect herbivory, a number of plant biochemical processes involved in the tolerance mechanism are affected. Different studies have demonstrated a diverse functional role of various plant oxidative enzymes in protecting plants against biotic stress induced by insect herbivory. Comprehensive profiling of stress-associated plant oxidative enzymes is most relevant to successful molecular breeding of stress-tolerant crop plants. Thus, better understanding of the biochemical basis of plant defense mechanisms is imperative, not only from a basic science perspective, but also for biotechnology-based pest control practice. In this review, we emphasize the potential role of various oxidative enzymes in plant defense against insect herbivory.
The development of local early basal resistance (EBR), is a form of non-specific general defence response of plants to bacteria, greatly depending on temperature. This symptomless defence mechanism is easily detected by its inhibitory action on the hypersensitive response (HR) caused by a subsequent incompatible pathogenic bacterium. Both EBR and HR were investigated at different temperatures ranging from 30 °C to 5 °C. At normal temperatures (30-20 °C) both heat-killed Pseudomonas syringae pv. syringae 61 (polyvirulent to many plants) and Pseudomonas savastanoi pv. phaseolicola S21 (pathogenic to bean) induced EBR in tobacco leaves within a few hours, but below 10 °C it was greatly delayed and at 5 °C usually no EBR response could be detected within 2-3 days. The time required for development of EBR did not depend on the bacterial pathovars or strains. However, the induction time of HR was not as sensitive to low temperatures as that of EBR, instead, it depended on the bacterial pathovars used.
Plant resistance breeding has, so far, been based on specific resistance genes which regulate hypersensitive reaction, resulting in fast tissue destruction. Hungarian researchers have, however, discovered the existence of the
general defense system
), which regulates a completely different plant defense reaction. This manifests itself in tissue thickening through cell enlargement. We have studied the biochemical background of these different plant defense processes by OPLC, a forced-flow version of planar chromatography. We also exploited some basic well-known advantages of planar chromatography which made its application suitable and favorable in our experiments. As a result of analysis of time-dependent changes in carbohydrate compounds, we confirmed pathological and symptomatological observations that plants have both general and specific defense systems. These two systems have different roles and strategies in excluding pathogens, but together constitute the complete disease resistance of plants.
Nitrogen (N) is an important nutrient for plant growth and yield production, and rice grown in paddy soil mainly uses ammonium (NH4+) as its N source. Previous studies have shown that N status is tightly connected to plant defense; however, the roles of NH4+ uptake and assimilation in rice sheath blight disease response have not been studied previously. Here, we analyzed the effects of different N sources on plant defense against Rhizoctonia solani. The results indicated that rice plants grown in N-free conditions had higher resistance to sheath blight than those grown under N conditions. In greater detail, rice plants cultured with glutamine as the sole N source were more susceptible to sheath blight disease compared to the groups using NH4+ and nitrate (NO3–) as sole N sources. N deficiency severely inhibited plant growth; therefore, ammonium transporter 1;2 overexpressors (AMT1;2 OXs) were generated to test their growth and defense ability under low N conditions. AMT1;2 OXs increased N use efficiency and exhibited less susceptible symptoms to R. solani and highly induced the expression of PBZ1 compared to the wild-type controls upon infection of R. solani. Furthermore, the glutamine synthetase 1;1 (GS1;1) mutant (gs1;1) was more susceptible to R. solani infection than the wild-type control, and the genetic combination of AMT1;2 OX and gs1;1 revealed that AMT1;2 OX was less susceptible to R. solani and required GS1;1 activity. In addition, cellular NH4+ content was higher in AMT1;2 OX and gs1;1 plants, indicating that NH4+ was not directly controlling plant defense. In conclusion, the present study showed that the activation of NH4+ uptake and assimilation were required for rice resistance against sheath blight disease.
The flavonoid biosynthesis pathway yields a large family of phenolic compounds which are involved in many biological activities including plant defense response to a broad spectrum of abiotic and biotic stress factors. In recent years, a wide range of evidences of relationship between the flavonoid biosynthesis and stress has been accumulated based on genetic, physiological and biochemical studies. In this paper, possible mechanisms of counteraction of flavonoid substances to different stress factors are reviewed, and the evidences for relationship between biosynthesis of flavonoid compounds and response to biotic and abiotic stress are summarized with emphasis on cereals.
Basal resistance (BR, a local
resistance against pathogens induced by general elicitors) is a multi-faceted
defence mechanism appearing in many shapes and with many given names, such as
induced (acquired) resistance (protection, defence), as well as a part of
innate immunity. Here, we give a historical overview of concepts, present
results and an outlook associated with bacteriological studies in the Plant
Protection Institute (PPI). The topics on BR briefly covered are its elicitors,
light and temperature dependence, changes in plant physiology, transcription
and protein expression during it and its effect on bacteria. We emphasize the
importance and relevance of its quick form, early BR, which might be a plant
defence mechanism in nature against all kinds of pathogenic and saprophytic