Plants

bs148h 27 September 2007 Read: Text ch 29 & 30 • plant phylogeny & diversity • photosynthesis • light spectral sensitivity • alternation of generations multicellular gametophyte (n) & sporophyte (n) •nonvascular mosses etc. • vascular ferns etc • seed plants • flowering plants - sex • fruit and seed dispersal • chemical defenses ... and offenses!

Plant Diversity: Land plants evolved fromfreshwater green algae Diversity w/ many shared, derived traits - adaptations to life in land-air environment
fruit: Fig 38.9 & sec 38.2

flowering plants seeds plants (sec 30.1, 38.2) vascular plants w/ ‘plumbing’ (ch 35) land plants w/ fatty-waxy cuticle (Fig 36.12) & stomata (Fig 36.15) - conserve water

Fig. 29.4 & 29.7. The ‘Kingdom Plantae’ has been reduced to a sister clade of the greenalgae clade
modern Chara - a pond weed is in sister group to modern plants The mitochondrial genome of Chara vulgaris: Insights into the mitochondrial DNA architecture of the last common ancestor of green algae and land plants Turmel M, et al. PLANT CELL 15 (8): 1888-1903 AUG 2003

Photosynthesis (ch 10): Life is powered by sunshine. Every molecular O2 that we breath was once part of two H2Omolecules, liberated by photosynthesis. The captured energy is released from our food and fuel. Photosynthesis occurs in many bacteria and in chloroplasts of algae, as well as most plants; chloroplasts are ‘remains’ of ancestral prokaryotic endosymbionts. Photosynthesis uses light energy to split H2O, release O2, make ATP & NADPH, and ATP put the ‘hydrate’ in carbohydrate. 2 stages: 1a capturing energyfrom light (ch 10.2) w/ photopigment molecules: chlorophylls & carotenoids 1b using the energy to make reducing (electron accepting) NADPH energy-storing ATP 2 the Calvin cycle (ch 10.3): using ATP & NADPH to synthesize complex organic molecules: sugars: glucose C6H12O6 → starch, wood
1C6H12O6

What is in sunlight plants can use? (sec 10.2) Light is electromagnetic energy, ‘convenientlythought of as’ a wave. Shorter wavelengths carry greater energy Fig 10.6 Light visible to human retinal pigments is a small portion of the solar spectrum. {birds & insects see down into UV}

12H2O

6CO2

Cyanobacteria, green algae & plants Cyanobacteria, use chlorophyll a as main photopigment & chlorophyll b as an accessory Carotenoids absorbs blue-green – inefficeintly. Leaves look green becausechlorophyll does NOT absorb green - it absorbs red and violet. violet Note: carotenoids do not absorb orange-red
6O2

carotenoids chlorophyll b chlorophyll a

+

6H2O

Fig 10.9 Englemann’s brilliant 1882 experiment w/ aerobic bacteria distributing themselves along spyrogyra algae behind a prism

Plants have sensory systems and “behavioral” responses: to crowding Plant sensory systems(ch 39); red-light sensitive phytochrome (Fig 39.4, 39.20) exists in interconvertible forms: when Pr absorbs red (~660nm), switches to Pfr when Pfr absorbs far-red (~730nm), switches to Pr The concentration of Pfr influences stem elongation (etiolation) in shade. Note low ratio of red/far-red left in light passed through leaves (shade). red/ far(shade) Manipulative approaches to testing adaptiveplasticity: plasticity Phytochrome-mediated shade-avoidance responses Phytochromeshadein plants. {text ch 39.3} Schmitt et al. 1999. AM NAT 154:S43-S54. Because chlorophyll selectively absorbs red wavelengths, the ratio of red (R) to far-red (FR) wavelengths is an accurate signal of vegetation shade ... Many plants respond to low R:FR with a suite of photomorphogenic changes such as stem elongation,suppression of branching, altered biomass allocation, and accelerated flowering, commonly referred to as the "shade avoidance syndrome". Such responses are often elicited by FR reflected from neighboring plants before canopy closure, indicating that plants can detect and respond to potential future competitors … {bolt - race up high to compete for scarce light vs branch – spread out low to...