Background

Anthocyanins are red and purple pigments whose function in leaves is poorly understood. These

pigments often accumulate in stressed, juvenile, or senescent (e.g. autumn) leaves. One

hypothetical role is photoprotection, or blocking excess light from damaging leaves. This

damage can lead to reduced photosynthesis, a phenomenon called photoinhibition. Other

hypotheses include protection from insect herbivores and disease. However, anthocyanins are

metabolically costly to produce, and they may block some usable light. Blocking of light could

lead to comparatively lower photosynthesis in low light conditions.

Research ObjectiveExamine the effects of anthocyanin accumulation on photosynthesis, photoinhibition, and leaf herbivory and disease using three crop species.

Acknowledgements

I thank Mary Canady and Jeremy Tardiff for use of a plot at the Bowdoin Organic Garden. I also thank Mike and Lucretia Woodruff for loaning a plot on their farm. Thank you to Jack

O’Brien for advice on organizing data, and to Fedco Seeds for donating seed. This project was funded by the Bowdoin Life Sciences Fellowship.

Herbivory and Disease

• I collected data weekly for plants at two sites over the course of several weeks. Damage

from disease/class of herbivores was recorded as the proportion of leaves affected by a

certain type of damage.

• Two plots were established to diversify the herbivore and disease pressures plants

experience.

o Bowdoin Organic Garden: In a suburban environment. Herbivores associated with lawns,

such as leafhoppers and oriental beetles, were predicted to be more common.

o Milkweed Farm: In an agricultural setting surrounded by woodland. Herbivores that

commonly attack crop plants, such as flea beetles and cabbage white caterpillars, were

predicted to be more common.

• Data is shown for fully expanded leaves at the Bowdoin Organic Garden on July 24, 2015

• Green lettuce shows higher disease damage than red lettuce (Fig 1, Sidak’s post hoc, t(53) =

2.25, p < 0.0001); other species have low levels of disease. May be evidence for protection

against disease.

• Flea beetle damage was significantly higher in green variety of kale (Fig 1, Sidak’s post hoc,

t(53) = 2.25, p = 0.005). This is possible evidence for anthocyanins repelling flea beetles.

(Note: Flea beetle damage was much more common at Milkweed Farm, and preliminary data

analysis suggests green lettuce was more affected than red lettuce.)

• There were no consistent trends for damage from leafhoppers and other herbivores.

• On-going data analysis will take into account temporal and site differences.

Examining Functional Roles for Anthocyanins in Plant Leaves

Benjamin M. West; Advisors: Barry Logan and Jaret Reblin

Red Kale Green Kale Red Lettuce Green Lettuce Red Shiso Green Shiso Bicolored* Shiso*green upper side of leaf, red underside

Photosynthesis and Photoprotection

• Photosynthesis was measured as CO2 uptake at various light intensities.

Degree of photoinhibition was quantified using a chlorophyll-fluorescence

based measurement of photosystem II (PSII) efficiency.

• There was no significant differences between varieties regarding the light

intensity at which net photosynthesis equals zero (Figs 2A-C, two-way ANOVA,

F(1, 24) = 0.004, p > 0.9). This does not support hypothesis of detrimental

light blocking by anthocyanins.

• There was a higher maximum photosynthetic rate in green lettuce than red

lettuce (Sidak’s post-hoc, t(24) = 3.43, p = 0.007) . This would not be due to

anthocyanins blocking light.

• There were no signs of photoinhibition in any variety (Fig 2D, Fv/Fm > 0.8)

and no differences in maximum PSII efficiency between red and green

varieties (Fig 2D, two-way ANOVA, F(1, 78) = 0.77, p = 0.4). Anthocyanin

accumulation appeared to confer no additional photoprotection in these crop

species under sunny field conditions.

• Bicolored shiso had lower max PSII efficiency than red shiso (Fig 2D, Tukey’s

post-hoc after a one-way ANOVA, p = 0.004). This does not seem to be an

anthocyanin-related difference.

Figure 2. Plots of photosynthetic rates at varying light intensities for red- and

green-leafed crop plants (A – C) and maximum photosystem II efficiency for the

same plants measured after a sunny day. n.s. = not significantly different; values

with different letters above them are significantly different.

● = green, ● = red, ● = bicolor

Conclusions

• Anthocyanins may play a role in repelling flea beetles and decreasing disease

susceptibility. Trends regarding damage from other herbivores are currently unclear

but may become apparent as more data is analyzed.

• Anthocyanin accumulation does not appear detrimental to photosynthesis at low

light levels.

• Neither red nor green crop plants become photoinhibited under sunny summer

conditions. If anthocyanins are providing a photoprotective role in red plants, other

photoprotective mechanisms must be equally active in the green plants.

Figure 1. Average proportions of fully expanded leaves of crop plants affected by various types of

damage. Statistical differences within plant species shown. n.s. = not significantly different; values

with different letters above them are significantly different at a value of p ≤ 0.05, and pairs of bars

with a star over them are significantly different from each other at a value of p ≤ 0.05.

● = green, ● = red, ● = bicolor