PBL- WHEN NATURE

STRIKES

Group members:

Wong Siew Ching D20091034815

Chew Mei Ping D20091034816

Ong Shwu Chyn D20091034817

Yee Hon Kit D20091034822

Ngang Huey Chi D20091034861

TBF 3023Plant Physiology

HOW CACTUS AND BROMELIADS CAN GROW WELL UNDER DRY CONDITION?

Cacti -most water-resourceful plants in the world Pineapple- highly tolerant of drought.

Drought tolerant refers to the degree to which a plant is adapted

to arid or drought conditions. drought tolerant plants typically make use of

either C4 carbon fixation / crassulacean acis metabolism (CAM) to fix carbon during photosynthesis.

Both cactus and bromeliads are CAM plants.

WHAT ARE THE CHARACTERISTIC OF CACTUS AND BROMELIADS?

THE CHARACTERISTICS THAT HELP THEM TO SURVIVE IN DROUGHT.

Cactuses Criteria Bromeliads

Leaves on most cacti are absent or extremely tiny

Leaves ~The epidermis of leaf is especially thick and tough to resist damage and desiccation.~A special layer of water storage cells on the underside of the leaf that act as a reserve in times of water stress~have tiny scales on their leaves called trichomes.

The cactus stem serves as the plant's main photosynthetic organ and is used for water storage

Stem Have distinctive, water-absorbing scales

. Their thinness and large surface area

make the scales ideal for rapidly absorbing

water.

Cactuses Criteria Bromeliads

Cactus roots help to gather and preserve water in several ways .

Roots Able to resist wilting

open their stomates at night rather than during the day in hot or dry climates(CAM Photosynthesis)

Stomata Opens its stomata during the night rather than the daytime(CAM Photosynthesis)

•Spines•Skin

Others •Xerophytes

BROMELIADS LEAVES Unique shape and arrangement of the leaves of

bromeliads. Wide and deeply U-shaped where they join the stem,

forming a series of vessel-like compartments. When it rains, water flows down the leaves and pools in

the compartments, where it can be absorbed by the umbrella scales.

Remarkable "tank plants" - Nidularium and Billbergia. Greatly reduced stem & densely packed leaves have broad, overlapping bases, resulting in a pitcher or vase-like center-the tank. Rainwater fills the tank ,as the tank is shaded by the dense crown of leaves around it, the water does not evaporate quickly and can persist, enabling the plant to survive periods of drought

CACTUSES ROOTS

Shallow & extensive root systems Spread laterally away from the plant. Maximize water intake from a large area.

Change characteristics as the water supply fluctuates. Existing dehydrated roots become more water

conductive after rainfall. Formation of new rain roots to help soak up water. In times of drought, the rain roots shrivel and fall

off .The existing roots dehydrate. The shrinkage of the existing roots creates an air gap

that helps to prevent water in the roots from escaping back to the soil.

A corky layer on the roots also helps to prevent water loss.

SPINES OF CACTUS Spines help the cactus in several ways.

Protection against foragers. Water from dew condenses on spines and, in some

cactus species, downward-pointing spines help to direct rainwater to the roots of the plant.

Reflect light away from the cactus stem theoretically lowering the stem temperature.

Trap in a layer of air next to the cactus stem preventing loss of water via evaporative cooling.

SKIN OF CACTUS

Translucent & acts as the first line of defense against fungi, bacteria, and foraging animals.

The skin has two parts: the epidermis and the hypodermis. The skin's hypodermis layer provides mechanical support for

the plant. A waxy layer of cells known as the cuticle covers the

skin’s epidermis. The wax in the cuticle helps the stem to hold in its water

vapor reducing water loss. Waxy cuticle is also lightly colored and reflects some of the

incident light. Contains numerous stomata

(However, is less than the number for normal plants - another water-saving characteristic.)

XEROPHYTES Possess many of the usual, water-conserving

adaptations of such plants: A thick epidermis covered with wax Water-storage cells that cause the leaves to

appear succulent (that is thick and fleshy Sheathing leaf bases.

Light Dependent Reactions

Non-cyclic photophosphorylation

Cyclicphotophosphorylation

Light Independent Reaction:

Calvin Cycle

HATCH – SLACK PATHWAY

Only occurs in C4 plants and CAM plants.

COMPARISON BETWEEN C3 , C4 , AND CAM PLANTS

EXAMPLES

C3 plants C4 plants CAM plantsTomatoLegumeTobaccoWheat

SugarcaneMaizeSorghumEleusine

CactusBromeliad

CO2 FIXATION AND CO2 ACCEPTOR

C3 plants C4 plants CAM plants

Once, only in mesophyll cells.

Twice, first in mesophyll cells and then in bundle sheath cells.

Once, only in mesophyll cells.

Ribulose biphosphate RuBP (5C) –mesophyll cells

Phosphoenelpyruvate PEP (3C) -mesophyll cellsRibulose biphosphate RuBP (5C) –bundle sheath cells

Phosphoenelpyruvate PEP (3C) -mesophyll cells

ENZYME AND FIRST PRODUCT FORMED

C3 plants C4 plants CAM plants

RuBP carboxylase-inefficient at low CO2 concentration.

PEP carboxylase-high affinity for CO2 at low concentration

RuBP carboxylase-efficient at high CO2 concentration.

PEP carboxylase-high affinity for CO2 at low concentration

Glycerate 3-phosphate (GP), a C3 acid.

Oxaloacetate, a C4 acid.

Oxaloacetate, a C4 acid.

PHOTORESPIRATION

CO2+RuBP(5C) 2G3P (3C) O2+RuBP(5C) phosphoglycorate (2C)+G3P

(3C) Phosphoglycorate was the react with O2 to

form CO2 with no production of energy Is wasteful

PHOTORESPIRATION-O2 IS USED, CO2 IS RELEASED

C3 plants C4 plants CAM plants

Occurs.Oxygen acts as competitive inhibitor.

Inhibited by high concentration of CO2.Light intensity & temperature are higher, O2 is not a competitive inhibitor.

Inhibited by high concentration of CO2.

EFFICIENCY OF PHOTOSYNTHESIS

C3 plants C4 plants CAM plants

Less efficient photosynthesis than C4 plant.Yields usually lower.

Photosynthesis more efficient.Yields are usually much higher.

Photosynthesis more efficient.

LEAF ANATOMY

C3 plants C4 plants CAM plants

Two distinct tissues:•palisade cell•mesophyll cellKrantz anatomy absent1 type of chloroplast in mesophyll cellsVascular bundle packed tightly, many chloroplasts

Vascular bundle surrounded by two rings of cells:•mesophyll cell•bundle sheath cellThinner than C3 plant

Krantz anatomy absent 1 type of chloroplast in mesophyll cells

CROSS-SECTIONS OF LEAVES FROM C3 AND C4 PLANTS.

THANK YOU..