Plant death

Signs Initially, leaves may have a thin white line but eventually become slightly yellowed (chlorotic). The vascular tissue is damaged and leaves begin to die from the edges towards the midrib, ultimately resulting in plant death. It has the capacity to destroy whole fields in a few months. ... 

Dicamba (3,6-dichloro-2-methoxybenzoic acid) is primarily used as a postemergence broadleaf herbicide, which interferes with normal plant auxin function, subsequently causing uncontrolled growth and the inhibition of the phototropic and geotropic function. Cumulative response results in plant death. The success of auxinic analogues such as Dicamba and 2,4-dichloropheno-xyacetic acid in weed control has led to widespread manufacturing and use. Estimated U.S. production for Dicamba was 5 million kg in 1990 [391]. 

Cyclic photophosphorylation is also a highly energetic reaction. The bipyridyliums, paraquat and diquat (Figure 2.2), divert the electron flow of cyclic photophosphorylation (photosystem I). The capture of an electron from the chlorophyll reduces the herbicide and the reduced herbicide reacts with oxygen to form superoxide. Superoxide produces hydrogen peroxide within the chloroplast and these two compounds interact to form hydroxyl radicals in the presence of an iron catalyst. Hydroxyl radicals are very damaging and lead to the destruction of the cellular components leading to rapid plant death. 

The enzyme p-hydroxyphenylpyruvate dioxygenase is involved in the conversion of p-hydroxyphenylpyruvate into homogentisate, a key step in plastoquinone biosynthesis. Inhibition of this enzyme has an indirect effect on carotenoid biosynthesis as plastoquinone is a co-factor of the enzyme phytoene desaturase. The new maize herbicide isoxaflutole and the triketone herbicides such as sulcotrione (Figure 2.7), inhibit p-hydroxyphenylpyruvate dioxygenase and this leads to the onset of bleaching in susceptible weeds and ultimately plant death.4... 

This mode of action has been shown to be very effective at controlling weeds with rates as low as 1 gha-1 leading to plant death for two good reasons. In the first place, there is little substrate competition with the herbicide because the substrate is lost to the cytoplasm when inhibition occurs and, second, because protoporphyrin IX will accumulate even... 

How would you show that a herbicide that inhibited photosynthesis required light to show its effect and that plant death was not due to starvation ... 

Lethal amounts in meri stems halting cell division and resulting in plant death... 

ALS is the first common enzyme in the biosynthetic route to valine, leucine and isoleucine. It is the site of action for the triazolopyrimidine (TP) herbicides as well as the sulfonylureas (SU) and imidazolinones (IM). These compounds act on the meristem and are slow to bring about plant death. 

Since TP, SU and IM are slow to bring about plant death, there are significant opportunities to exploit metabolism of the herbicide to influence crop tolerance. Metabolism has indeed been the overriding parameter determining crop selectivity (5c.16.17). ALS inhibiting herbicides in development and/or full commercialization are known to have selectivities to all the major crops including corn, soybeans, wheat, barley, rice, cotton and canola. 

Disease rating 0-no symptoms, 1-leaf stem lesions, 3-plant death. lesions only. 2-leaf and... 

Drought, or too little water, can cause wilting, along with leaf scoreh (browned leaf edges), early fruit or leaf drop, stem dieback, and plant death. 

Many diseases and insects through premature senescence or plant death can indirectly affect soybean seed quality. Soybean rust, caused by Phakopsora pachyrhizi, attacks soybean leaves primarily, but not seed, leading to defoliation and early senescence. Yield losses are due to a reduction in seed number and seed size. Seed size losses of 12 to 20% can occur (Arias et al., 2005 Dupleich et al., 2005). 

Blockage of electron transport on the reducing side of PS II is just the first in a series of steps that ultimately leads to plant death. Much of the energy from absorbed photons that is normally directed into electron transport is redirected into fluorescence and triplet formation when the herbicides are bound. The triplet states are of special interest because of the destructive interaction between excited chlorophyll and molecular oxygen through the following four step mechanism, where... 

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