Mehler reaction (1951): in chloroplast (PS1), O2 → H2O2 Oxygen uptake: Dark respiration: in mitochondria water production, CO2 release ATP production inhibitor: KCN Photorespiration: in chloroplast, peroxisome, mitochondria oxygen cycle, CO2 release ATP consume inhibitor: DCMU decreased photosynthetic efficiency Alternative respiration: Mehler reaction (1951): in chloroplast (PS1), O2 → H2O2 No CO2 release promote photosynthetic efficiency

The dural function of water-water cycle: 1. scavenging active oxygen, then reinforce the CO2 assimilation 2. safe dissipation of excess photon energy lighting Mehler

Plants respire roughly half of the daily photosynthetic yield ¤ Respiration rate depends on the species and growth habit of the plant, the type and age of the specific organ, and environmental variables, such as temperature, nutrient and water supply. Whole plant: on a fresh-weight basis: generally lower than animal’s rate isolated plant mitochondria: as fast as or faster than mammalian mitochondria Plants respire roughly half of the daily photosynthetic yield tropic plants: higher normal respiration (consumption of 70~80% daily PS gain) younger vs. older trees (photosynthetic/nonphotosynthetic tissues)  lose 1/3 vs. 2/3 of their photosynthate as respiration Photosynthesis rate (Max.)  Photorespiration rate  normal respiration rate [chloroplast] [C, M, peroxisome] [mitochondria] Different tissues and organs respire at different rates

Environmental factors alter respiration rate : P. 277 ~ 278 O2: the Km for oxygen of cytochrome c oxidase is below 1 M the oxygen concentration of aqueous solution is 250 M (21% O2 in air) water saturation, flooded (diffusion limitation)  [O2] hydroponic culture: O2 supply aerenchyma: intercellular air spaces from leaves to roots pneumato(de)phores, trees that grow in mangrove, swamps temperature: T, respiration rate  ( 0 to 30°C) Q10, short-term; if long-term, acclimated [commercial Q10] too low, decreased respiration rate, stimulated stored starch degradation  optimum storage temperature (7~9 °C for potato), too high or low CO2: 3 to 5%, inhibit respiration (optimum storage: low temp, low [O2]) enrichment ? artificial biosphere’s result: [CO2], respiration rate/biomass (?)

Cytoplasmic male sterility (cms): p. 276 the presence of distinct rearrangements in their mtDNA, a non-Mendelian fashion do not form a viable pollen, prevent self-pollination example: a unique 13-kDa protein, URF13 in cms line of maize + Hm-T-toxin is produced by fungus Bipolaris maydis (Cochliobolus heterostrophus)  produce pores in the inner Mito. Membrane, loss selectivity, corn leaf blight Nowadays: mechanical detasseling, which prevents self-pollination.

Lipid : Two type of glycerolipids 1. triacylglycerols, the fats (saturated FA) and oils (unsaturated FA),  are stored in oil bodies of most seeds (lipase hydrolysis)  are converted into carbohydrates in germinating seeds 2. glycerolipids (phospholipase x hydrolysis)  the main structural lipids in membrane  two types: glyceroglycolipids and glycerolphospholipids  are precursors of important signaling compounds

Lipid bodies, referred to as osmiophilic bodies or plastoglobules, are ubiquitous structures in the stroma.

Plastoquinone Tocopherols (vit E)