No abstract

Gall-inducing insects produce various types of galls on plants, but little is known about the gall-induction mechanism of these galling insects. The gall wasp Leptocybe invasa Fisher & LaSalle (Hymenoptera: Eulophidae) forms galls of different sizes on several Eucalyptus species. To clarify the physiological responses of Eucalyptus to L. invasa infestation, we measured the dynamics of nitrogen (N), carbon (C), total phenolics, total tannins and four types of phytohormones (zeatin [Z] + zeatin riboside [ZR], gibberellins [GA], indole-3-acetic acid [IAA] and abscisic acid [ABA]) in galled and ungalled leaf tissues of two Eucalyptus horticultural varieties (DH201-2 [Eucalyptus grandis × Eucalyptus camaldulensis] and EA [Eucalyptus exserta]) with different susceptibility to galling throughout the larval developmental stages. Nitrogen, total phenolics, tannins and four kinds of phytohormones strongly accumulated in tissues galled by L. invasa (especially during early larval feeding stages). While N, Z + ZR and GA levels were higher, tannins and ABA levels were lower in the galled tissues on the highly susceptible variety. Nitrogen, total phenolics, GA, Z + ZR and IAA levels in the galled tissues gradually decreased during gall development, but ABA and tannins conversely increased in the galled tissues of the less susceptible variety. Our results suggest that the effects of gall-inducing insects on plants depend not only on the susceptibility of the plant infested but also on the developmental stage of galled tissues. Gall formation process is thus synergistically influenced by both gall-inducing insect and plant genotypes.

We aimed to determine whether humic acid (HA) can alleviate the injury of millet caused by drought and its potential mechanism. Millet seeds (Jingu 21 and Zhangza 10) were soaked in different concentrations of HA (0, 50, 10, 200, and 300 mg L −1 ) for 12 h. The physiological and photosynthetic characteristics of millet seedlings, including growth parameters, osmotic regulators, antioxidase activity, photosynthesis, chlorophyll fluorescence, and P700 parameters, were determined before and after drought stress. HA significantly promoted the growth of millet seedlings under drought stress. Pretreatment with 100 mg L −1 or 200 mg L −1 HA significantly increased free proline, soluble protein, and activity of the antioxidant enzyme system (superoxide dismutase, peroxidase, and catalase) in both Zhangza 10 and Jingu 21. The accumulation of reactive oxygen species (O � :2 and H 2 O 2 ) was reduced in HA treatments compared with that of the control (P < .05). Moreover, HA (100 mg L −1 ) significantly increased net photosynthetic rate, stomatal conductance, effective quantum yield of photosystem II, relative photosynthetic electron transfer rate of photosystem II, and photochemical quenching. HA also reduced intercellular CO 2 concentration and non-photochemical quenching. Furthermore, 200 mg L −1 HA significantly increased the maximum P 700 , effective quantum yield of photosystem I, and relative photosynthetic electron transfer rate of photosystem I in Zhangza 10 and decreased non-photochemical energy dissipation in Jingu 21 and Zhangza 10 under drought stress. HA promoted the growth of millet seedlings under drought stress by promoting the osmotic adjustment ability and antioxidant capacity of seedlings and increased photosynthesis.

To explore the role of Brassinolide (BR) in improving the tolerance of Sigma Broad in foxtail millet (Setaria italica L.), effects of 0.1 mg/L of BR foliar application 24 h before 3.37 g/ha of Sigma Broad treatment at five-leaf stage of foxtail millet on growth parameters, antioxidant enzymes, malondialdehyde (MDA), chlorophyll, net photosynthetic rate (P N), chlorophyll fluorescence and P700 parameters were studied 7 and 15 d after herbicide treatment, respectively. Results showed that Sigma Broad significantly decreased plant height, activities of superoxide dismutase (SOD), chlorophyll content, P N, PS II effective quantum yield (Y (II)), PS II electron transport rate (ETR (II)), photochemical quantum yield of PSI(Y (I)) and PS I electron transport rate ETR (I), but significantly increased MDA. Compared to herbicide treatment, BR dramatically increased plant height, activities of SOD, Y (II), ETR (II), Y (I) and ETR (I). This study showed BR pretreatment could improve the tolerance of Sigma Broad in foxtail millet through improving the activity of antioxidant enzymes, keeping electron transport smooth, and enhancing actual photochemical efficiency of PS II and PSI.

In order to assess its response to the herbicide, sethoxydim (SEY), seedlings of two foxtail millet (Setaria italica) hybrids were exposed to 0.75, 1.5, 3, and 6 L(SEY active ingredient, ai) ha -1 for 7 and 15 d. Our results showed that SEY reduced photosynthesis and oxidative stress in the hybrid millet (Zhangza) at the dosage below 1.5 L(ai) ha -1 (i.e., recommended dosage), whereas it caused death of Jingu 21 at all treatment dosages. In addition, we further explored the effect of SEY on PSI and PSII; the hybrid millet showed a greater tolerance to SEY and also the ability to recover. In conclusion, the hybrid millet seems to possess certain photosynthetic protection mechanisms which could reduce or eliminate the herbicide stress by increasing nonphotochemical quenching for dissipating excessive light energy under SEY-induced oxidative stress.