Age, Fluence Rate, and Anthocyanin Production in Zea mays Seedlings

Increase in fluence rates of white light over the range of 5to 80 µmol m^–2 s^–1 brought about a correspondingincrease in amounts of anthocyanin production in shoots of Zeamays L. seedlings. Roots also exhibited a similar relationshipbetween increased fluence rate and increased anthocyanin productionover the range of 5 to 40 µmol m^–2 s^–1 whereasfluence rates above 40 µmol m^–2 s^–1 broughtabout decreases in anthocyanin production. Rates of productionand amounts of accumulation of anthocyanin in both shoots androots were found to vary with the age of the seedlings at thetime of exposure to light. Age, fluence rates, anthocyanin, seedlings, Zea mays     

Impaired Anthocyanin Production in Barbiturate treated Zea mays Seedlings

Anthocyanin production was impaired in both roots and shootsof Zea mays seedlings germinated on 1 and 2 mM concentrationsof four barbiturates having different lipid/aqueous partitioncoefficients. The severity of impaired anthocyanin productionwas greater in those seedlings treated with the higher lipidsoluble barbiturates irrespective of the concentrations used.Indirect evidence is presented which indicates that barbituratesinterfere with normal membrane physiology responsible for anthocyaninproduction. Anthocyanin, barbiturate, seedlings, Zea mays     

The role of calcium in salt toxicity

Salt toxicity comprises osmotic and ionic components both of which can severely affect root and shoot growth. Uptake of Na⁺ across the plasma membrane is very fast resulting in physiological effects on extracellular as well as intracellular sites. Sodium reduces binding of Ca²⁺ to the plasma membrane, inhibits influx while increasing efflux of Ca²⁺, and depletes the internal stores of Ca²⁺ from endomembranes. These changes in the cell Ca²⁺ homeostasis are suggested here to be the primary responses to salt stress that are perceived by root cells. Salt would almost instantly reduce the amount of Ca²⁺ being transferred to the leaf cells, with Ca²⁺ activity dropping and Na⁺ activity rising in the apoplasm of leaf cells. This Ca²⁺ signal would be transported to leaves together with, if not preceding, the signal of limited water supply. Hormonal signals are likely to be secondary in nature and caused by the Na⁺-related disturbance of the root cell Ca²⁺ homeostasis. Ameliorative effects of supplemental Ca²⁺ on salt stress are exerted through preventing Na⁺-related changes in the cell Ca²⁺ homeostasis.     

Chlorsulfuron Reduces Extension of Wheat Root Tips in Low-zinc Solution Culture

Root tip extension was used as a measure of wheat root responseto exposure to the sulfonylurea herbicide chlorsulfuron. Plantspre-grown in low-zinc (0.2 µMZnHEDTA) solutions were placedin a perspex chamber with nutrient solution on both sides ofa partition separating the root tip from the rest of the plant.The root tip was exposed to different concentrations of chlorsulfuronand observations were made during 22 h. Increasing the concentrationof zinc in the solution around the root tip to 4 µMZnHEDTAdid not alter root tip extension in the absence of chlorsulfuron.Significant decreases in root growth after 22 h were obtainedwith concentrations of 120 µg chlorsulfuron l^-1and greater.Increasing the Zn concentration from 0.2 to 20 µMZnHEDTAin the nutrient solution around the root tip decreased controlroot growth but stimulated chlorsulfuron-treated roots to extendat the same rate as chlorsulfuron-free control plants. AddingZn and chlorsulfuron to the more mature root parts above theroot tip partition did not significantly influence root tipextension. It is concluded that chlorsulfuron inhibits wheatroot growth and that increased Zn concentrations can alleviateor prevent the deleterious effects of chlorsulfuron.Copyright1998 Annals of Botany Company Wheat,Triticum aestivumL., chlorsulfuron, root growth, zinc.     

Genotypic Differences in the Production and Partitioning of Carbohydrates Between Roots and Shoots of Wheat Grown under Zinc or Manganese Deficiency

The partitioning of soluble carbohydrates and starch betweenroots and shoots was investigated in wheat genotypes differingin Zn or Mn efficiency. The plants were grown for 11 d in achelate-buffered nutrient solution with sufficient or deficientZn and Mn supply. The Zn-efficient cultivar Warigal had a greatershoot fresh weight under sufficient Zn compared with the Zn-inefficientcultivar Durati. When supplied with sufficient Zn, Warigal hada greater concentration and content of soluble carbohydratesin roots and shoots in comparison with Durati. Under deficientZn supply, Durati had a greater concentration and content ofstarch in roots and shoots compared with Warigal. In an experimentwith varying supply of Mn, the Mn-efficient genotype C8MM hada greater shoot fresh weight than the Mn-inefficient cultivarBayonet under sufficient or deficient Mn supply. The concentrationof soluble carbohydrates in roots and shoots was decreased bydeficient Mn supply in C8MM but not in Bayonet. Starch accumulatedin the roots of Bayonet under deficient Mn supply. The resultssuggest that synthesis of carbohydrates is decreased under Zndeficiency, while they are preferentially partitioned to theroots to increase growth and thus the surface area availablefor Zn uptake. In the case of Mn deficiency, carbohydrate productionwas limited, but partitioning between roots and shoots was notaltered.Copyright 1997 Annals of Botany Company Carbohydrate; deficiency; manganese; assimilate partitioning; starch; Triticum aestivum; zinc     

Disturbance of cell Ca2+ homeostasis as a primary trigger of Al toxicity syndrome

The primary toxic effects of Al are fast (taking only seconds to several minutes to develop). These effects may be due to the presence of Al ions on the apoplasmic side of the plasma membrane; Al ions may not need to enter the cytosol for a range of primary deleterious Al effects to occur. Aluminium may disturb the symplasmic Ca²⁺ homeostasis by altering the pattern of Ca²⁺ fluxes across the plasma membrane. Disturbance of transmembrane Ca²⁺ fluxes may prevent an increase in cytosolic Ca²⁺ activity necessary to trigger spindle formation during prophase as well as to initiate the metaphase/anaphase transition. The mechanism behind Al-related inhibition of mitosis and polar cell growth is suggested to be disturbance of stimulus/response coupling effected through Ca²⁺ as a second messenger. Involvement of calmodulin in the Al-related phenomena could be indirect, at least in the initial stages of the Al treatment when Al is probably confined to the apoplasm only. Al-related disturbance of the Ca²⁺ homeostasis in the cytosol would alter the patterns of Ca²⁺ -calmodulin binding, resulting in the absence of activation or only partial activation of calmodulin.     

Aluminium Effects on Pollen Germination and Tube Growth of Chamelaucium uncinatum. A Comparison with Other Ca2+Antagonists

An interaction between aluminium (Al) and calcium (Ca) may bea cause of Al toxicity in plants. The pollen tube is a suitablesystem to test the interaction between Al and Ca since Ca ionsplay a pivotal role in pollen germination and tube growth. Weinvestigated how Al and other known blockers of Ca²⁺-permeablechannels (trivalent cations, ruthenium red, verapamil and nifedipine)influence pollen of an Australian native species Geraldton waxflower(Chamelaucium uncinatum). Pollen germination was inhibited bymicromolar concentrations of trivalent cations (La³⁺>Al³⁺>Gd³⁺)and ruthenium red, but it was relatively insensitive to a micromolarconcentration of verapamil. Exposure of the growing pollen tubesto micromolar concentrations of Al³⁺and La³⁺, and a millimolarconcentration of Ca²⁺chelator ethyleneglycol-bis(ß-aminoethylether)-N,N'-tetraacetic acid (EGTA) led to rapid tip bursting.In contrast, exposure to Gd³⁺, nifedipine, ruthenium red, verapamiland the organic trivalent cation tris (ethylenediamine)cobalt(TEC³⁺) caused only inhibition of pollen tube growth. The Al³⁺-relatedpollen tube bursting was reduced significantly by increasingeither solution pH from 4.5 to 6 or activity of Ca²⁺from 0.25to 5 m M. In contrast, La³⁺-related pollen tube bursting wasinsensitive to changes in Ca²⁺activity. The results are discussedin terms of Al interactions with cell wall Ca²⁺and the plasmamembrane Ca²⁺-permeable channels. Copyright 1999 Annals of BotanyCompany Aluminium toxicity, Ca²⁺-channel blockers, cell wall, Chamelaucium uncinatum, pollen germination, pollen tube growth.     

Micronutrient Deficiency Influences Plant Growth and Activities of Superoxide Dismutases in Narrow-leafed Lupins

The effect of copper (Cu), zinc (Zn) or manganese (Mn) deficiencyon the growth and activity of superoxide dismutase (SOD) formswas investigated in seedlings of narrow-leafed lupins (LupinusangustifoliusL.). Plants grown without Zn developed Zn deficiencysymptoms 24 d after sowing (DAS), and those grown without Mnshowed Mn deficiency symptoms 31 DAS. However, plants grownwithout Cu did not show visible leaf symptoms. Shoot dry weightwas decreased by Zn and Mn deficiency 24 DAS, and by Cu deficiency31 DAS. Soluble protein concentration was reduced considerablyby Zn deficiency 24 DAS, but was not affected by Cu deficiencyuntil 31 DAS. In contrast, soluble protein concentration inMn-deficient plants was higher than in control plants 31 DAS.Shoot concentration of micronutrients which were not suppliedto plants decreased significantly, with a simultaneous increasein concentration of one or more of the other nutrients analysed.The activities of total SOD, MnSOD and Cu/ZnSOD on a fresh weightbasis declined drastically in -Cu and -Zn plants 24 DAS. Onthe contrary, the activities of total SOD and Cu/ZnSOD on eithera fresh weight or soluble protein basis increased markedly in-Mn plants 24 DAS, and MnSOD activity increased significantlyin these plants 31 DAS. It was concluded that micronutrientdeficiency (Cu, Zn or Mn) altered the activities of SOD formsdepending on the kind and severity of the deficiency stress.Manipulation of the capacity of plants to tolerate oxidativestress may influence their capacity to tolerate micronutrientdeficiency.Copyright 1999 Annals of Botany Company. Copper,Lupinus angustifolius, manganese, deficiency, superoxide dismutase, zinc.