26. Photosynthesis Inhibitors: Triazines And Ureas

Front 1

how are photosynthesis inhibitors more toxic to plants than animals in contrast to inhibitors of respiration?

Back 1

only plants have chloroplast and photosynthesis
compounds interfere with respiration (mitochondria) act on most living organisms

Front 2

how does the photosynthetic machinery chain in chloroplast work? (how do electrons flow?)

Back 2

electrons flow from PS II to Rieske iron sulfur protein to PS I and in presence of light ADP is phosphorylated to ATP

Front 3

Which herbicides inhibit photosynthesis and where?

Back 3

PS II (in Qb1): metribuzin (type of triazinone), atrazine (type of triazine), diuron (ureas)

PSI: diquat, paraquat

Front 4

A mutation of serine to glycine at the Qb1 binding site confers resistance to which herbicide?

Back 4

atrazine

Front 5

What is the importance of triazines in terms of domestic use?

Back 5

use dominated by atrazine, use in corn and sorghum as preemergent for broadleafs and some grassy weeds
used as preemergent and postemergent herbicide, effective at low doses in killing broadleaf weeds in corn and other crops and in high doses, as soil sterilants
low mammalian toxicity and wildlife toxicity except moderate for CN compds
strong inhibitors of photosynthesis

Front 6

atrazine is a selective herbicide for what types of weeds for which crops?

Back 6

weeds: broadleaf and grassy weeds

crops: sorghum, corn

Front 7

why must atrazine be used under conditions where nitrosamine derivatives are not formed?

Back 7

don't use atrazine in fertilizer or will form nitrosamine, its a mutagen

Front 8

how is atrazine synthesized?

Back 8

look at figs in p. 208

Front 9

what is structure of atrazine and how metabolized?

Back 9

look at fig p. 209

Front 10

how does metabolism of atrazine differ in tolerant vs sensitive plants?

Back 10

tolerant plants able to metabolize atrazine to hydroxyatrazine, very unstable form that falls apart to make amines and CO2

sensitive plants- atrazine not metabolized, accumulates in plant, cause chlorosis(no CO2, fixation, sugar and starch not form and plant dies

Front 11

how oes atrazine behave in soils and what are toxicological properties?

Back 11

readily bound to collodial soil particles in clay and muck soils, susceptible to loss from volatilization and UV decomposition

properties: very low tox to fish and birds
reported to be potent in altering frog development
low acute and chronic tox to mammals

Front 12

how do triazine analogs compare in terms of characteristics such as water solbuility, persistance, selectivity, biodegradability, and safety for crops?

Back 12

simazine: ver low water solubility, very persistant in soil to give season long control

atrazine: more water soluble, absorb through roots and leaves, preand post emergent activity

alkoxy compounds; higher water solubility, effective via leaves and roots but less selective (prometon)

methylthiocompounds: readily oxidize to sulfoxides and sulfones, more biodegradible and shorter persistance, sulfoxides react with GSH-GSH-S transferase system, (dimetryn, terbutryn, prometryn)

Front 13

what are uses and mechanism of action of ureas?

Back 13

use- substituents influence water and soil binding, activity is general
used for cotton and soybean

Front 14

What is diuron? how is it metabolized? what is its behavior in soils?

Back 14

diuron- dimethyl area
used on preemergence or directed postemergence at .6-6.4 lb/acre for germinating boradleaf and grass weeds
metabolism: in plants, translocated up xylem, metabolism removes one methyl group, then second, then CO-N cleavage to give aniline and CO2, also some ring hydrozylation

breakdown in soil promarily microbial with little loss by photodecomposition or volality

Front 15

what crop is propanil used for? why cant you use it with OP or MC?

Back 15

used for rice

dont use with OP or MC or rice will lose its ability to be resistant to propanil (inhibit amidase) p. 211

Front 16

what are carotenoids? what is function in chlorophyll?

Back 16

caroteniod- red or yellow pigment, in chloroplast, trap light of wavelength not absorbed by chlorophyll, protect cell against photosensitized oxidations

Front 17

how do carotenoid biosnthesis inhibitor destroy chlorophyll?

Back 17

destroy indirectly by causing photooxidation

Front 18

describe process of carotenoid biosynthesis

Back 18

melavonic acid -> isopentenylpyrophosphate (IPP) -> dimethylallylpyrophosphate => gernaylpyrophosphate => phytoene
-> with desaturase wil make phytofluene -> carotene

Front 19

site of carotein biosynthesis inhibiton?
examples of inhibitors?

Back 19

inhibit phytoene desaturase with m-trifluoromethylphenyl derivative (like fluoridine,fluorochloridone) , make phytoene accumulate

inhibit IPP isomerase with chlomazone, which decreases carotenoids, chlorophylls and GA

zeta caroteine desaturase- inhibit by dichlormate and 6 methylpyrimidines, make zeta carotene accumulate

lycopene to alpha and beta carotene inhibit by amitrole

Front 20

what is amitroles effect on growth at low and high levels?

Back 20

low: stimulate growth
high: inhibite growth by inhibit photosynthesis on blocking carotenoid synthesis