Indol-3yl-acetic acid in roots of Zea mays

Indol-3yl-acetic acid was identified in extracts of sterile roots of Zeamays seedlings by means of TLC, chromogenic reactions, GLC and GC-MS.     

Enzymatic removal of zeins from the surface of maize starch granules

Alcohol-extractable, hydrophobic zein proteins contaminate starch granule surfaces and can be removed by enzymatic digestion with thermolysin. The goal of this research was to find practical alternatives to thermolysin that might be used during the corn wet-milling process. All of the commercial thermostable alkaline proteases studied (SP 709, Neutrase, and Spezyme FAN) removed the zein proteins from various types of cornstarch, as demonstrated by the lack of protein bands below 30 kDa under the reducing conditions of SDS-PAGE gel. Each enzyme removed the zein proteins as effectively as thermolysin removed them. However, the removal of the zein protein did not reduce the quantity of free fatty acids associated with the starch. Journal of Industrial Microbiology & Biotechnology (2000) 24, 71–74. Received 27 May 1999/ Accepted in revised form 01 October 1999     

Maize nicotinate N-methyltransferase interacts with the NLR protein Rp1-D21 and modulates the hypersensitive response

Most plant intracellular immune receptors belong to nucleotide-binding, leucine-rich repeat (NLR) proteins. The recognition between NLRs and their corresponding pathogen effectors often triggers a hypersensitive response (HR) at the pathogen infection sites. The nicotinate N-methyltransferase (NANMT) is responsible for the conversion of nicotinate to trigonelline in plants. However, the role of NANMT in plant defence response is unknown. In this study, we demonstrated that the maize ZmNANMT, but not its close homolog ZmCOMT, an enzyme in the lignin biosynthesis pathway, suppresses the HR mediated by the autoactive NLR protein Rp1-D21 and its N-terminal coiled-coil signalling domain (CC_D21). ZmNANMT, but not ZmCOMT, interacts with CC_D21, and they form a complex with HCT1806 and CCoAOMT2, two key enzymes in lignin biosynthesis, which can also suppress the autoactive HR mediated by Rp1-D21. ZmNANMT is mainly localized in the cytoplasm and nucleus, and either localization is important for suppressing the HR phenotype. These results lay the foundation for further elucidating the molecular mechanism of NANMTs in plant disease resistance.     

PROTEIN RETENTION IN THE ENDOPLASMIC RETICULUM OF INSECT CELLS IS NOT COMPROMISED BY BACULOVIRUS INFECTION

High level expression of the major auxin-binding protein (ABP1) from maize (Zea maysL.) has been used to demonstrate that the machinery for retaining proteins in the endoplasmic reticulum (ER) of insect cells functions efficiently throughout the baculovirus infection cycle. Immuno-localization showed wild-type ABP1 (ABP1-KDEL) to be targeted to the lumen of the ER, in accordance with its signal peptide and carboxyterminal KDEL ER-retention signal. The protein accumulated in dilations of the ER, and none was detected at the cell surface. Immunoblotting of concentrated culture medium confirmed that ABP1-KDEL was not secreted at a detectable level. In contrast, when the carboxyterminus was mutated to KEQL, secretion of the baculovirus-expressed protein was readily detected. Immunolocalization and immunoblotting demonstrated that a high proportion of the ABP1-KEQL protein was secreted at the cell surface and into the culture medium. The data demonstrate that the ER of insect cells has a great capacity to retain proteins and that this property is largely unaffected by the cellular disruption caused by baculovirus replication.     

The effect of soil aggregate size on early growth and shoot-root ratio of maize (Zea mays L.)

Shoot dry mass and leaf area of 16-d old maize plants decreased as soil aggregate size in greenhouse pots increased in diameter from 0.075–0.5 to 4–8 mm. Root length was also much greater on the finer aggregate beds, due primarily to increased growth of second-order laterals. In a subsequent experiment in which shoot dry matter again decreased with increasing aggregate size, it was found that a similar change in root morphology as noted in experiment I resulted in increased root dry mass as aggregate size increased. The associated change in shoot-root ratio was significant eight days after emergence. This change was due to a change in allocation of fixed carbon rather than allocation of seed reserves. Neither transpiration rate per unit leaf area, nor net assimilation rate were affected by aggregate size. Likewise nutrition could not account for the differences in shoot or root growth.     

Polyamine oxidase from Zea mays shoots

Polyamine oxidase of maize shoots purified 10-fold had a pH optimum of 6·3 with spermidine as substrate, and K_m of 6 × 10^?4 M. The enzyme was inhibited by the acridine compounds quinacrine, 6,9-diamino-2-ethoxyacridine and acriflavin, but carbonyl reagents, typical thiol inhibitors and copper-binding agents were without effect. Inhibition by quinacrine was reversed by FMN and FAD. Furthermore, about 50 % of the activity of the apoenzyme was restored by the addition of FAD, but not by FMN or riboflavin, indicating that the maize polyamine oxidase is an FAD-dependent flavoprotein.     

Modulation of photosystem 2 reactions mediated by aluminium toxicity in Zea mays

Two weeks old maize (Zea mays L. cv. XL-72.3) plants were submitted to 0 to 81 g m-3 Al for 20 d in a growth medium of low ionic strength. The increasing Al concentrations sharply increased chlorophyll (Chl) concentrations. The rates of photosystem 2 activities (H2O→DCPIP and DPC→DCPIP) increased at 9 g(Al) m-3 but at higher Al doses they decreased again. A slight decrease of qE and qN coupled to an increase of qP was also observed until the 27 g m-3 Al. The Al-induced decline in cytochrome (cyt) b contents per Chl unit was parallel for the b559LP and cyt b559HP forms, but on a leaf area basis more or less opposite trend in both these cyt forms was observed. Increased Al concentrations also decreased carotene and zeaxanthin contents. This revised version was published online in June 2006 with corrections to the Cover Date.