Modification of leaves

Leaves are often modified to perform functions other than photosynthesis.

Succulent leaves are also thickened leaves, but they are found above ground, still conduct photosynthesis, and function primarily in water storage

Spines are sharp projections derived from leaves that function in plant defense. Almost all cacti (in the plant family Cactaceae)  barberry and some Acacia species have spines 

Spines can also be formed from stipules (stipular spines) or bud scales.

Tendrils are another structure that can originate from multiple structures, including stems, leaves, or leaflets. 

leaves of glory lily are modified as tendrils

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Plant pathogens are divided into three groups

Biotrophs derive energy from living cells, they are found on or in living plants, can have very complex nutrient requirements and do not kill host plants rapidly;

Necrotrophs derive energy from killed cells; they invade and kill plant tissue rapidly and then live saprotrophically on the dead remains;

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Hemibiotrophs have an initial period of biotrophy followed by necrotrophy.

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Biotrophs are Specialised (‘obligate’) pathogens

Possess appressoria or haustoria

Narrow host range

Controlled by salicylate-dependent host-defence pathways

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Biotrophic fungi usually penetrate the rigid cell wall via the formation of a specialized infection structure on the plant

surface called an appressorium. Then, the emerging penetration

peg breaches the rigid plant cell wall and provides entry into the plant cell. Finally, a haustorium forms upon entry into the plant cell.

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Necrotrophs are Opportunistic, unspecialised (‘non-obligate’) pathogens and Host cells killed rapidly

Entry unspecialised via wounds or natural openings

Secrete copious cell-wall-degrading (lytic) enzymes and toxins

Appressoria/haustoria not normally produced

Wide host range

Easy to culture axenically

Survive as competitive saprotrophs

Controlled by jasmonate- and ethylene-dependent host-defence pathways