Plant lecture 1 - organisation of plant metabolism

Question 1

Plant organisation/structure

Answer 1

• Vacuole = 95-98% of cell volume. separates from cytosol by tonoplast
• Adjacent cells are connected w/ plasmodesmata. Allows free diffusion of small compounds up to 8kDa btw cells
• Apoplasm = space outside plasma membrane where material can diffuse freely

Question 2

Carbohydrate flexibility/oxidation

Answer 2

• Plants use ↑ range of carbohydrates as respiratory substrates
• Sucrose, metabolic flexibility
• Starch in plastid or fructans in vacuole
• Other C sources e.g. raffinose

Question 3

Experiment

Varying response to developmental requirements

Answer 3

• 14C supplied to exiled maize root tips + different sections of root tip separated + fractionated
• Co2 contains ↓ proportion of 14C, acidic compounds the most
• Different components synthesised in different proportion in each section

Question 4

Experiment

Alternative metabolic pathways

Answer 4

• 14C experiments
• DHAP + G3P = mirrors (1-3) (6-4)
• C3+4 = COOH in pyruvate → CO2 in TCA
• Rest = acetyl coA
• Hypothetically, Cs are release 3/4, 2/5, 1/6
• C3/4 = labels in aa, so not just CO2 (must be another route for making organic aa → PEP carboxylase)
• C1+6 should be equivalent. C1 actually > C6 (alternative route for decarboxylation of glucose → PPP)
• C2 should > Co2 from C6 but x (alternative route for release of CO2 from C6 → UDP glucose)

Question 5

Experiment

Plants contain multiple isoforms

Answer 5

• Ion exchange chromatography column showed 2 peaks for PFK

Question 6

Carbohydrate oxidation isoforms

Answer 6

• Plastids + cytosol
• Encoded for by different genes
• Duplication occurs as compromise btw requirements in pathway (C oxidation needed for E source vs source of intermediates that can act as precursors (plastid))
• 2 roles could conflict, need pathway to be regulated in response to demand for both
• Translators that catalyser controlled exchange of specific intermediates