The stem defines the symptom precisely — the killing or collapse of tissues — so the answer is the term that names cell death rather than any other kind of injury.

Necrosis is exactly that: the death and collapse of leaf tissue, visible as dead patches that turn brown, tan or white and often become dry and brittle. Pollutants such as sulphur dioxide, ozone, fluorides and peroxyacetyl nitrate produce it, and the pattern of the dead areas is diagnostic — sulphur dioxide typically causes interveinal necrosis, while ozone causes stippling and flecking on the upper surface.

Chlorosis is the loss or failure of chlorophyll, so the leaf yellows while the tissue remains alive. It signals impaired photosynthesis, not tissue death, and a chlorotic leaf may recover if the stress is removed.

Abscission is the shedding of leaves at the abscission zone at the base of the petiole. It is the plant discarding an organ, an orderly separation rather than a collapse of tissue.

Epinasty is the downward bending or curling of leaves caused by unequal growth on the upper surface, commonly a response to ethylene. The leaf changes orientation but its cells stay alive.

Hence the effect that causes the killing or collapse of tissues is necrosis.