Occurrence, structure, and function of short cells in maize leaf epidermis.

Short cells are specialised epidermal cells of grasses and they include cork and silica cells. The time of occurrence, distribution, and number of short cells differ among plants or tissues of the same plant. The present study aimed to assess the occurrence, structure, and function of short cells in the epidermis of maize (Zea mays L.) leaves from cultivar "Zhengdan 958″ under field and potted experimental conditions. Results showed that short cells occurred synchronously in multiple maize leaves. Few short cells occurred at the base of the fifth leaf; most were found at the middle and base of the sixth leaf, and throughout the seventh leaf. The accumulation of K+ and H2O2 in cork cells changed periodically with stomatal opening and closure, which was consistent with the accumulation of K+ and H2O2 in subsidiary cells; whereas no accumulation was observed in silica cells. Moreover, photosynthetic parameters and stomatal aperture were significantly higher in leaves containing short cells than in those without them in the same parts of different leaves or in different leaves at the same leaf position. Accumulation of K+ and H2O2 in cork cells increased with increasing water stress. In conclusion, short cells not only improved leaf mechanical support and photosynthetic performance, and maize drought resistance, but they also participated in stomatal regulation.

H2O2, Ca2+, and K+ in subsidiary cells of maize leaves are involved in regulatory signaling of stomatal movement.

The stomata of maize (Zea mays) contain a pair of guard cells and a pair of subsidiary cells. To determine whether H2O2, Ca2+, and K+ in subsidiary cells were involved in stomatal movement, we treated four-week-old maize (Zhengdan 958) leaves with H2O2, diphenylene iodonium (DPI), CaCl2, and LaCl3. Changes in content and distribution of H2O2, Ca2+, and K+ during stomatal movement were observed. When exogenous H2O2 was applied, Ca2+ increased and K+ decreased in guard cells, while both ions increased in subsidiary cells, leading to stomatal closure. After DPI treatment, Ca2+ decreased and K+ increased in guard cells, but both Ca2+ and K+ decreased in subsidiary cells, resulting in open stomata. Exogenous CaCl2 increased H2O2 and reduced K+ in guard cells, while significantly increasing them in subsidiary cells and causing stomatal closure. After LaCl3 treatment, H2O2 decreased and K+ increased in guard cells, whereas both decreased in subsidiary cells and stomata became open. Results indicate that H2O2 and Ca2+ correlate positively with each other and with K+ in subsidiary cells during stomatal movement. Both H2O2 and Ca2+ in subsidiary cells promote an inflow of K+, indirectly regulating stomatal closure.

Mitochondrial Dysfunction Causes Oxidative Stress and Tapetal Apoptosis in Chemical Hybridization Reagent-Induced Male Sterility in Wheat.

Male sterility in plants has been strongly linked to mitochondrial dysfunction. Chemical hybridization agent (CHA)-induced male sterility is an important tool in crop heterosis. Therefore, it is important to better understand the relationship between mitochondria and CHA-induced male sterility in wheat. This study reports on the impairment of mitochondrial function duo to CHA-SQ-1, which occurs by decreasing cytochrome oxidase and adenosine triphosphate synthase protein levels and theirs activities, respiratory rate, and in turn results in the inhibition of the mitochondrial electron transport chain (ETC), excessive production of reactive oxygen species (ROS) and disruption of the alternative oxidase pathway. Subsequently, excessive ROS combined with MnSOD defects results in damage to the mitochondrial membrane, followed by ROS release into the cytoplasm. The microspores underwent severe oxidative stress during pollen development. Furthermore, chronic oxidative stress, together with the overexpression of type II metacaspase, triggered premature tapetal apoptosis, which resulted in pollen abortion. Accordingly, we propose a metabolic pathway for mitochondrial-mediated male sterility in wheat, which provides information on the molecular events underlying CHA-SQ-1-induced abortion of anthers and may serve as an additional guide to the practical application of hybrid breeding.

Hydrogen peroxide is involved in salicylic acid-elicited rosmarinic acid production in Salvia miltiorrhiza cell cultures.

Salicylic acid (SA) is an elicitor to induce the biosynthesis of secondary metabolites in plant cells. Hydrogen peroxide (H2O2) plays an important role as a key signaling molecule in response to various stimuli and is involved in the accumulation of secondary metabolites. However, the relationship between them is unclear and their synergetic functions on accumulation of secondary metabolites are unknown. In this paper, the roles of SA and H2O2 in rosmarinic acid (RA) production in Salvia miltiorrhiza cell cultures were investigated. The results showed that SA significantly enhanced H2O2 production, phenylalanine ammonia-lyase (PAL) activity, and RA accumulation. Exogenous H2O2 could also promote PAL activity and enhance RA production. If H2O2 production was inhibited by NADPH oxidase inhibitor (IMD) or scavenged by quencher (DMTU), RA accumulation would be blocked. These results indicated that H2O2 is secondary messenger for signal transduction, which can be induced by SA, significantly and promotes RA accumulation.

[Responses of stomata and Kranz anatomy of maize leaves to soil water shortages].

Seedlings of the popular maize cultivar "Zhengdan-958" growing in pots individually were exposed to suitable soil water conditions as control, light water shortage, moderate water shortage, and severe water shortage, corresponding to soil water contents between 75%-85%, 65%-75%, 55%-65%, and 45%-55% of field water capacity, respectively. Responses of stomatal aperture, Kranz anatomy, and vascular bundle structure to different water contents of maize leaves were investigated. Results showed that under increased water shortages, the levels of H2O2 in both guard cells and subsidiary cells were enhanced, also the fluorescence intensity of H2O2 labeled with fluorescent dye increased, while stomatal aperture and conductance decreased gradually. Moreover, Kranz cells were messily arranged and the cell size became smaller and smaller, and the structure of bundle sheath cells went irregular; and the sectional area of the big bundle and xylem, the cell number of phloem, and the thickness of whole leaf and of upper and lower epidermis reduced. In addition, the number of chloroplasts in mesophyll cells and vascular bundle sheath cells decreased, particularly under the moderate water deficit, chloroplasts in Kranz cells which located in the inside of cytoplasmic membrane and cling on the cell wall spread to the direction of cell center. It demonstrated that stomatal closing of maize could be regulated by H2O2 in guard cells and subsidiary cells together, and H2O2 in subsidiary cells maybe played a cooperative role. In conclusion, under increased soil water shortages, drought-induced H2O2 accumulations in both guard cells and subsidiary cells of maize leaves participated in the regulation of stomatal closing. And, the size of Kranz cells and bundle sheath cells, the cell number of phloem, and the area of the xylem and phloem re- duced, thereby, reducing water shortage-induced damage.

Drought-induced H2O 2 accumulation in subsidiary cells is involved in regulatory signaling of stomatal closure in maize leaves.

Increasing H2O2 levels in guard cells in response to environmental stimuli are recently considered a general messenger involved in the signaling cascade for the induction of stomatal closure. But little is known as to whether subsidiary cells participate in the H2O2-mediated stomatal closure of grass plants. In the present study, 2-week-old seedlings of maize (Zea mays) were exposed to different degrees of soil water deficit for 3 weeks. The effects of soil water contents on leaf ABA and H2O2 levels and stomatal aperture were investigated using physiological, biochemical, and histochemical approaches. The results showed that even under well-watered conditions, significant amounts of H2O2 were observed in guard cells, whereas H2O2 concentrations in the subsidiary cells were negligible. Decreasing soil water contents led to a significant increase in leaf ABA levels associated with significantly enhanced O2 (-) and H2O2 contents, consistent with reduced degrees of stomatal conductance and aperture. The significant increase in H2O2 appeared in both guard cells and subsidiary cells of the stomatal complex, and H2O2 levels increased with decreasing soil water contents. Drought-induced increase in the activity of antioxidative enzymes could not counteract the significant increase in H2O2 levels in guard cells and subsidiary cells. These results indicate that subsidiary cells participate in H2O2-mediated stomatal closure, and drought-induced H2O2 accumulation in subsidiary cells is involved in the signaling cascade regulating stomatal aperture of grass plants such as maize.

[Effects of Ca2+ on salicylic-acid induced biosynthesis of salvianolic acid B in young seedlings of Salvia miltiorrhiza Bunge].

In order to study the effects of Ca2+ in the biosynthesis of salvianolic acid B (Sal B) induced by salicylic acid (SA) in the young seedlings of Salvia miltiorrhiza, we used confocal laser scanning microscopy and high performance liquid chromatography to measure the change of relative fluorescence intensity of Ca2+ and the contents of Sal B induced by SA before and after the application of extracellular calcium channel inhibitors (VP and LaCl3), intracellular calcium channel inhibitor (LiCl), as well as intracellular calmodulin antagonist (TFP). SA could induce the calcium burst, and the Ca2+ peak could last to 2-3 min in the guard cells of S. miltiorrhiza, which prompted the biosynthesis of Sal B after the Ca2+ burst. Both Vp or LaCl3, and LiCl or TFP could inhibit the burst of Ca2+ and the biosynthesis of Sal B. The above results demonstrated that Ca2+ from the extracellular and the intracellular calcium store regulate the biosynthesis of Sal B elicited by salicylic acid in S. miltiorrhiz young seedlings.

Antitumour immunity mediated by mannan-modified adenovirus vectors expressing VE-cadherin.

Anti-angiogenesis represents an indispensible strategy for cancer therapy. As a strictly endothelial-specific adhesion molecule, vascular endothelial cadherin (VE-cadherin, VE-cad) is a promising anti-angiogenesis target. In this study a recombinant adenovirus vector modified with mannan was used to deliver VE-cad (AdVEC-m) and we tried to explore its feasibility as an antitumour agent in mouse cancer models. The immunogenic delivery of VE-cad resulted in obvious prophylactic and therapeutic inhibition of tumour growth and prolonged survival in mice. In the meantime angiogenesis declined apparently within the tumours measured by immunohistochemistry staining and coated alginate bead assay in vivo. Anti-VE-cad antibodies were identified by western blot analysis and enzyme-linked immunosorbent assay (ELISA). VE-cad-specific T lymphocyte cytotoxicity responses (CTL) were detected by chromium (51Cr) release assay of splenocytes from AdVEC-m treated mice. These results demonstrate that mannan modification is able to enhance antigen delivery and immune responses, and the way of immunogenic delivery (AdVEC-m) is expected to provide an attractive vaccine strategy for cancer immunotherapy.

[Effects of water deficit at seedling stage on maize root development and anatomical structure].

A pot experiment was conducted to study the effects of water deficit at seedling stage on the root development and anatomical structure of maize. Four treatments were installed, i.e., 75%-85% of field capacity (control), 65%-75% of field capacity (light deficit), 55%-65% of field capacity (moderate deficit), and 45%-55% of field capacity (heavy deficit). Drought stress inhibited the plant growth. With increasing drought stress, the root length, diameter, and total biomass reduced, while the root vigor, root/shoot ratio, and root apex polysaccharide content increased. Under moderate water deficit, the branch root hair length, root hair density, and total length of root hair reached to the maximum. Anatomical observation showed that the decrease of root diameter was mainly due to the decrease of root central cylinder area and of root vessel diameter. No significant difference was observed in the root vessel number among the treatments, but the root vessel wall became irregular under water deficit. The increase of root apex polysaccharide content mainly occurred in the epidermal cells and pileorhiza cells. In epidermis cells, the polysaccharide was mainly in dissociation, while in pileorhiza cells, polysaccharide was mainly as starch grains. In sum, under water deficit, maize root could alter its vessel structure, increase the polysaccharide content in epidermal cells and pileorhiza cells, and expand the total surface area of root hair to enhance the water-absorbing ability of hair root, and to strengthen the drought resistance of maize. However, with the increase of water deficit, root hair didn't have unrestrictive growth, while in adverse, its growth was inhibited or damaged under severe drought.